Date | Country | Change |
| 1966 |  Australia | Diocese of Maitland lost territory to Diocese of Lismore |
| 1966 | Australia,  Norfolk Island | Metropolitan Archdiocese of Sydney lost territory to Diocese of Maitland |
| 1966 |  France | Titular Episcopal See of Accia was restored |
| 1966 |  Italy | Titular Episcopal See of Amiterno was restored |
| 1966 | Italy | Titular Episcopal See of Arpi was established |
| 1966 | Italy | Titular Episcopal See of Blanda was restored |
| 1966 | Italy | Titular Episcopal See of Canne was restored |
| 1966 | Italy | Titular Episcopal See of Capo della Foresta was restored |
| 1966 | Italy | Titular Episcopal See of Claterna was restored |
| 1966 | Italy | Titular Episcopal See of Eclena was restored |
| 1966 | Italy | Titular Episcopal See of Equilio was restored |
| 1966 | Italy | Titular Episcopal See of Eraclea was restored |
| 1966 | Italy | Titular Episcopal See of Faleri was restored |
| 1966 | Italy | Titular Episcopal See of Fidene was restored |
| 1966 | Italy | Titular Episcopal See of Forconio was restored |
| 1966 | Italy | Titular Episcopal See of Foro Flaminii was restored |
| 1966 | Italy | Titular Episcopal See of Gabi was restored |
| 1966 | Italy | Titular Episcopal See of Lilibeo was restored |
| 1966 | Italy | Titular Episcopal See of Malamocco was restored |
| 1966 | Italy | Titular Episcopal See of Martana was established |
| 1966 | Italy | Titular Episcopal See of Monterano was restored |
| 1966 | Italy | Titular Episcopal See of Nomento was restored |
| 1966 | Italy | Titular Episcopal See of Pausula was established |
| 1966 | Italy | Titular Episcopal See of Pesto was restored |
| 1966 | Italy | Titular Episcopal See of Plestia was restored |
| 1966 | Italy | Titular Episcopal See of Roselle was restored |
| 1966 | Italy | Titular Episcopal See of Sabiana was restored |
| 1966 | Italy | Titular Episcopal See of Salpi was restored |
| 1966 | Italy | Titular Episcopal See of Subaugusta was restored |
| 1966 | Italy | Titular Episcopal See of Sulci was restored |
| 1966 | Italy | Titular Episcopal See of Treba was restored |
| 1966 | Italy | Titular Episcopal See of Tricala was restored |
| 1966 | Italy | Titular Episcopal See of Tronto was restored |
| 1966 | Italy | Titular Episcopal See of Velia was established |
| 1966 | Italy | Titular Episcopal See of Voghenza was restored |
| 1966 | Italy | Titular Episcopal See of Volturno was established |
| 1966.01.03 |  Iran | Archdiocese of Ahvaz (Chaldean Rite) was established (from Metropolitan Archdiocese of Sehna and without ecclesiastical province) |
| 1966.01.03 |  Turkiye | Diocese of Diarbekir (Chaldean Rite) was promoted as Archdiocese of Diarbekir |
| 1966.01.10 |  Uruguay | Diocese of Maldonado–Punta del Este was established (from Diocese of Minas and became suffragan of Montevideo) |
| 1966.01.10 |  USA | Apostolic Exarchate of United States of America (Maronite Rite) was established |
| 1966.01.10 | USA | Apostolic Exarchate of United States of America (Greek-Melkite Rite) was established |
| 1966.01.22 | USA | Metropolitan Archdiocese of Anchorage was established (from Diocese of Juneau and with suffragan sees Fairbanks and Juneau) |
| 1966.02.01 |  Uganda | Diocese of Kabale was established (from Diocese of Mbarara and became suffragan of Rubaga) |
| 1966.02.15 |  Senegal | Apostolic Prefecture of Saint-Louis du Sénégal was promoted as Diocese of Saint-Louis du Sénégal (became suffragan of Dakar) |
| 1966.02.15 |  South Korea | Diocese of Masan 마산 was established (from Diocese of Busan 부산 and became suffragan of Daegu 대구) |
| 1966.03.10 |  Congo-Kinshasa | Diocese of Kabinda lost territory to Diocese of Kamina |
| 1966.03.10 | Congo-Kinshasa | Diocese of Kongolo lost territory to Diocese of Kabinda |
| 1966.03.25 |  Mexico | Diocese of Mexicali was established (from Diocese of Tijuana and became suffragan of Hermosillo) |
| 1966.04.25 | Mexico | Territorial Prelature of Madera was established (from Metropolitan Archdiocese of Chihuahua, Diocese of Ciudad Juárez and Diocese of Ciudad Obregón and became suffragan of Chihuahua) |
| 1966.04.26 | France | Metropolitan Archdiocese of Chambéry was renamed as Metropolitan Archdiocese of Chambéry–Saint-Jean-de-Maurienne–Tarentaise (gained territory from the suppressed Diocese of Saint-Jean-de-Maurienne and Diocese of Tarentaise and lost suffragan sees Saint-Jean-de-Maurienne and Tarentaise) |
| 1966.04.26 | France | Diocese of Saint-Jean-de-Maurienne was suppressed (to Metropolitan Archdiocese of Chambéry–Saint-Jean-de-Maurienne–Tarentaise) |
| 1966.04.26 | France | Diocese of Tarentaise was suppressed (to Metropolitan Archdiocese of Chambéry–Saint-Jean-de-Maurienne–Tarentaise) |
| 1966.04.30 |  Venezuela | Diocese of Barquisimeto was promoted as Metropolitan Archdiocese of Barquisimeto (with suffragan see Guanare) |
| 1966.04.30 | Venezuela | Diocese of Maracaibo was promoted as Metropolitan Archdiocese of Maracaibo (with suffragan see Cabimas) |
| 1966.05.03 | Congo-Kinshasa | Metropolitan Archdiocese of Luluabourg lost territory to Diocese of Mbujimayi |
| 1966.05.03 | Congo-Kinshasa | Apostolic Administration of Mbuji-Mayi was promoted as Diocese of Mbujimayi (gained territory from Metropolitan Archdiocese of Luluabourg and became suffragan of Luluabourg) |
| 1966.05.03 |  Equatorial Guinea | Apostolic Vicariate of Río Muni was promoted as Diocese of Bata (without ecclesiastical province) |
| 1966.05.03 | Equatorial Guinea | Apostolic Vicariate of Fernando Poo was promoted as Diocese of Santa Isabel (without ecclesiastical province) |
| 1966.05.16 |  Brazil | Diocese of Caxias exchanged territory with Diocese of Passo Fundo |
| 1966.05.16 | Brazil | Diocese of Passo Fundo exchanged territory with Diocese of Caxias |
| 1966.05.29 |  Portugal | Military Vicariate of Portugal was established |
| 1966.05.30 | Congo-Kinshasa | Metropolitan Archdiocese of Léopoldville was renamed as Metropolitan Archdiocese of Kinshasa |
| 1966.05.30 | Congo-Kinshasa | Metropolitan Archdiocese of Stanleyville was renamed as Metropolitan Archdiocese of Kisangani |
| 1966.05.30 | Congo-Kinshasa | Metropolitan Archdiocese of Elisabethville was renamed as Metropolitan Archdiocese of Lubumbashi |
| 1966.05.30 | Congo-Kinshasa | Metropolitan Archdiocese of Coquilhatville was renamed as Metropolitan Archdiocese of Mbandaka |
| 1966.06.07 | Australia | Apostolic Vicariate of Kimberleys was promoted as Diocese of Broome |
| 1966.06.07 |  Nigeria | Apostolic Prefecture of Maiduguri was promoted as Diocese of Maiduguri (became suffragan of Kaduna) |
| 1966.06.16 |  India | Diocese of Visakhapatnam lost territory to Diocese of Cuttack and Apostolic Prefecture of Raipur |
| 1966.06.21 |  Cook Islands,  Niue | Apostolic Vicariate of Cook Islands was promoted as Diocese of Rarotonga (gained territory from Apostolic Vicariate of Tonga Islands and Niue and became suffragan of Wellington) |
| 1966.06.21 |  Fiji | Apostolic Vicariate of Fiji Island was promoted as Metropolitan Archdiocese of Suva (with suffragan see Tarawa) |
| 1966.06.21 |  French Polynesia,  Pitcairn Islands | Apostolic Vicariate of Tahiti Islands was promoted as Metropolitan Archdiocese of Papeete (with suffragan see Taiohae) |
| 1966.06.21 | French Polynesia | Apostolic Vicariate of Marquesas Islands was promoted as Diocese of Taiohae (became suffragan of Papeete) |
| 1966.06.21 |  Kiribati,  Nauru | Apostolic Vicariate of Gilbert Islands was promoted as Diocese of Tarawa (became suffragan of Suva) |
| 1966.06.21 |  New Caledonia | Apostolic Vicariate of Nouvelle-Calédonie was promoted as Metropolitan Archdiocese of Nouméa (with suffragan sees Port-Vila and Wallis et Futuna) |
| 1966.06.21 |  Samoa | Apostolic Vicariate of Samoa Island and Tokelau was promoted as Diocese of Apia |
| 1966.06.21 |  Tonga | Apostolic Vicariate of Tonga Islands and Niue was promoted as Diocese of Tonga (lost territory to Diocese of Rarotonga and without ecclesiastical province) |
| 1966.06.21 |  Vanuatu | Apostolic Vicariate of New Hebrides was promoted as Diocese of Port-Vila (became suffragan of Nouméa) |
| 1966.06.21 |  Wallis and Futuna | Apostolic Vicariate of Wallis et Futuna was promoted as Diocese of Wallis et Futuna (became suffragan of Nouméa) |
| 1966.06.25 | USA | Diocese of Beaumont was established (from Diocese of Galveston–Houston and became suffragan of San Antonio) |
| 1966.06.29 |  Colombia | Diocese of Buga was established (from Metropolitan Archdiocese of Cali and Diocese of Palmira and became suffragan of Cali) |
| 1966.06.30 |  Peru | Diocese of Ayacucho was promoted as Metropolitan Archdiocese of Ayacucho (with suffragan sees Huancavélica and Caravelí) |
| 1966.06.30 | Peru | Diocese of Huancayo was promoted as Metropolitan Archdiocese of Huancayo (with suffragan sees Huánuco and Tarma) |
| 1966.06.30 | Peru | Diocese of Piura was promoted as Metropolitan Archdiocese of Piura (with suffragan sees Chachapoyas, Chiclayo, Chota and Chulucanas) |
| 1966.07.11 |  Philippines | Territorial Prelature of Davao was promoted as Diocese of Davao |
| 1966.07.11 | USA | Metropolitan Archdiocese of Saint Paul was renamed as Metropolitan Archdiocese of Saint Paul and Minneapolis |
| 1966.07.25 |  Spain | Metropolitan Archdiocese of Toledo (Mozarabic Rite) lost territory to Diocese of Albacete |
| 1966.08.05 |  Botswana | Apostolic Prefecture of Bechuanaland was promoted as Diocese of Gaberones (became suffragan of Bloemfontein) |
| 1966.08.05 | Uganda | Diocese of Jinja was established (from the suppressed Metropolitan Archdiocese of Rubaga and became suffragan of Kinshasa) |
| 1966.08.05 | Uganda | Diocese of Kampala was promoted as Metropolitan Archdiocese of Kampala (with suffragan sees Arua, Gulu, Masaka, Mbarara, Moroto and Tororo and gained territory from the suppressed Metropolitan Archdiocese of Rubaga) |
| 1966.08.05 | Uganda | Metropolitan Archdiocese of Rubaga was suppressed (to Metropolitan Archdiocese of Kampala and to establish Diocese of Jinja) |
| 1966.09.15 | USA | Diocese of Sacramento lost territory to Diocese of Stockton |
| 1966.09.29 | India | Diocese of Baroda was established (from Metropolitan Archdiocese of Bombay and became suffragan of Bombay) |
| 1966.10.07 | Venezuela | Diocese of San Felipe was established (from Metropolitan Archdiocese of Barquisimeto and Diocese of Valencia and became suffragan of Barquisimeto) |
| 1966.10.09 | France | Diocese of Corbeil was established (from Diocese of Versailles and became suffragan of Paris) |
| 1966.10.09 | France | Diocese of Créteil was established (from Metropolitan Archdiocese of Paris and Diocese of Versailles and became suffragan of Paris) |
| 1966.10.09 | France | Diocese of Nanterre was established (from Metropolitan Archdiocese of Paris and Diocese of Versailles and became suffragan of Paris) |
| 1966.10.09 | France | Diocese of Pontoise was established (from Diocese of Versailles and became suffragan of Paris) |
| 1966.10.09 | France | Diocese of Saint-Denis was established (from Metropolitan Archdiocese of Paris and Diocese of Versailles and became suffragan of Paris) |
| 1966.10.11 | Brazil | Diocese of Anápolis was established (from Metropolitan Archdiocese of Goiânia and became suffragan of Goiânia) |
| 1966.10.11 | Brazil | Diocese of Brasília was promoted as Metropolitan Archdiocese of Brasília (with suffragan sees Paracatu, Uruaçu and Formosa) |
| 1966.10.11 | Brazil | Diocese of Ipameri was established (from Metropolitan Archdiocese of Goiânia and became suffragan of Goiânia) |
| 1966.10.11 | Brazil | Diocese of Itumbiara was established (from Metropolitan Archdiocese of Goiânia and became suffragan of Goiânia) |
| 1966.10.11 | Brazil | Territorial Prelature of Miracema do Norte was established (from Diocese of Porto Nacional and became suffragan of Goiânia) |
| 1966.10.11 | Brazil | Territorial Prelature of Rubiataba was established (from Diocese of Goiás and Diocese of Uruaçu and became suffragan of Goiânia) |
| 1966.10.19 | Brazil | Diocese of Caxias was renamed as Diocese of Caxias do Sul |
| 1966.10.21 |  Thailand | Diocese of Bangnokhuek was renamed as Diocese of Ratburi |
| 1966.11.07 | Brazil | Diocese of Jundiaí was established (from Metropolitan Archdiocese of Campinas and Metropolitan Archdiocese of São Paulo and became suffragan of São Paulo) |
| 1966.11.07 | Philippines | Territorial Prelature of Bayombong was established (from Diocese of Tuguegarao and became suffragan of Nueva Segovia) |
| 1966.11.15 |  Indonesia | Apostolic Prefecture of Manokwari was promoted as Diocese of Manokwari (became suffragan of Merauke) |
| 1966.11.15 | Indonesia | Apostolic Vicariate of Merauke was promoted as Metropolitan Archdiocese of Merauke (with suffragan sees Manokwari and Sukarnapura) |
| 1966.11.15 | Indonesia | Apostolic Vicariate of Sukarnapura was promoted as Diocese of Sukarnapura (became suffragan of Merauke) |
| 1966.11.15 |  Papua New Guinea | Apostolic Vicariate of Aitape was promoted as Diocese of Aitape (became suffragan of Madang) |
| 1966.11.15 | Papua New Guinea | Apostolic Vicariate of Yule Island was promoted as Diocese of Bereina (became suffragan of Port Moresby) |
| 1966.11.15 | Papua New Guinea | Apostolic Vicariate of Northern Solomon Islands was promoted as Diocese of Bougainville (became suffragan of Rabaul) |
| 1966.11.15 | Papua New Guinea | Apostolic Prefecture of Daru was promoted as Diocese of Daru (became suffragan of Port Moresby) |
| 1966.11.15 | Papua New Guinea | Apostolic Vicariate of Goroka was promoted as Diocese of Goroka (became suffragan of Madang) |
| 1966.11.15 | Papua New Guinea | Apostolic Vicariate of Kavieng was promoted as Diocese of Kavieng (became suffragan of Rabaul) |
| 1966.11.15 | Papua New Guinea | Apostolic Vicariate of Lae was promoted as Diocese of Lae (became suffragan of Madang) |
| 1966.11.15 | Papua New Guinea | Apostolic Vicariate of Alexishafen was promoted as Metropolitan Archdiocese of Madang (with suffragan sees Aitape, Goroka, Lae, Mendi, Mount Hagen, Vanimo and Wewak) |
| 1966.11.15 | Papua New Guinea | Apostolic Vicariate of Mendi was promoted as Diocese of Mendi (became suffragan of Madang) |
| 1966.11.15 | Papua New Guinea | Apostolic Vicariate of Mount Hagen was promoted as Diocese of Mount Hagen (became suffragan of Madang) |
| 1966.11.15 | Papua New Guinea | Apostolic Vicariate of Port Moresby was promoted as Metropolitan Archdiocese of Port Moresby (with suffragan sees Bereina, Daru and Sideia) |
| 1966.11.15 | Papua New Guinea | Apostolic Vicariate of Rabaul was promoted as Metropolitan Archdiocese of Rabaul (with suffragan sees Bougainville, Gizo, Honiara and Kavieng) |
| 1966.11.15 | Papua New Guinea | Apostolic Vicariate of Samarai was promoted as Diocese of Sideia (became suffragan of Port Moresby) |
| 1966.11.15 | Papua New Guinea | Apostolic Prefecture of Vanimo was promoted as Diocese of Vanimo (became suffragan of Madang) |
| 1966.11.15 | Papua New Guinea | Apostolic Vicariate of Wewak was promoted as Diocese of Wewak (became suffragan of Madang) |
| 1966.11.15 |  Solomon Islands | Apostolic Vicariate of Western Solomon Islands was promoted as Diocese of Gizo (became suffragan of Rabaul) |
| 1966.11.15 | Solomon Islands | Apostolic Vicariate of South Solomons was promoted as Diocese of Honiara (became suffragan of Rabaul) |
| 1966.11.28 | Philippines | Diocese of San Pablo was established (from Diocese of Lipa and became suffragan of Manila) |
