Date | Country | Change |
| 1951 |  Syria | Titular Episcopal See of Palmyra (Greek-Melkite Rite) was restored |
| 1951 | | Titular Episcopal See of Pentacomia was suppressed |
| 1951.01.11 |  Eswatini | Apostolic Vicariate of Swaziland was promoted as Diocese of Bremersdorp (became suffragan of Pretoria) |
| 1951.01.11 |  Lesotho | Apostolic Vicariate of Basutoland was promoted as Diocese of Maseru (became suffragan of Bloemfontein) |
| 1951.01.11 |  South Africa | Apostolic Vicariate of Aliwal was promoted as Diocese of Aliwal (lost territory to establish Metropolitan Archdiocese of Bloemfontein and became suffragan of Cape Town) |
| 1951.01.11 | South Africa | Apostolic Vicariate of Bethlehem was promoted as Diocese of Bethlehem (became suffragan of Bloemfontein) |
| 1951.01.11 | South Africa | Metropolitan Archdiocese of Bloemfontein was established (from Apostolic Vicariate of Aliwal and Apostolic Vicariate of Kimberley in South Africa and with suffragan sees Bethlehem, Keimoes, Kimberley, Kroonstad and Maseru) |
| 1951.01.11 | South Africa | Apostolic Vicariate of Cape Town was promoted as Metropolitan Archdiocese of Cape Town (with suffragan sees Aliwal, Oudtshoorn, Port Elizabeth and Queenstown) |
| 1951.01.11 | South Africa | Apostolic Vicariate of Natal was promoted as Metropolitan Archdiocese of Durban (with suffragan sees Eshowe, Kokstad, Mariannhill and Mthatha) |
| 1951.01.11 | South Africa | Apostolic Vicariate of Eshowe was promoted as Diocese of Eshowe (became suffragan of Durban) |
| 1951.01.11 | South Africa | Apostolic Vicariate of Johannesburg was promoted as Diocese of Johannesburg (became suffragan of Pretoria) |
| 1951.01.11 | South Africa | Apostolic Vicariate of Keimoes was promoted as Diocese of Keimoes (became suffragan of Bloemfontein) |
| 1951.01.11 | South Africa | Apostolic Vicariate of Kimberley in South Africa was promoted as Diocese of Kimberley (lost territory to establish Metropolitan Archdiocese of Bloemfontein and became suffragan of Bloemfontein) |
| 1951.01.11 | South Africa | Apostolic Vicariate of Kokstad was promoted as Diocese of Kokstad (became suffragan of Durban) |
| 1951.01.11 | South Africa | Apostolic Vicariate of Kroonstad was promoted as Diocese of Kroonstad (became suffragan of Bloemfontein) |
| 1951.01.11 | South Africa | Apostolic Vicariate of Lydenburg was promoted as Diocese of Lydenburg (became suffragan of Pretoria) |
| 1951.01.11 | South Africa | Apostolic Vicariate of Mariannhill was promoted as Diocese of Mariannhill (became suffragan of Durban) |
| 1951.01.11 | South Africa | Apostolic Vicariate of Umtata was promoted as Diocese of Mthatha (became suffragan of Durban) |
| 1951.01.11 | South Africa | Apostolic Vicariate of Oudtshoorn was promoted as Diocese of Oudtshoorn (became suffragan of Cape Town) |
| 1951.01.11 | South Africa | Apostolic Vicariate of Port Elizabeth was promoted as Diocese of Port Elizabeth (became suffragan of Cape Town) |
| 1951.01.11 | South Africa | Apostolic Vicariate of Pretoria was promoted as Metropolitan Archdiocese of Pretoria (with suffragan sees Bremersdorp, Johannesburg, Lydenburg and Pietersburg) |
| 1951.01.11 | South Africa | Apostolic Vicariate of Queenstown was promoted as Diocese of Queenstown (became suffragan of Cape Town) |
| 1951.01.27 |  Egypt | Apostolic Vicariate of Egypt was renamed as Apostolic Vicariate of Alexandria of Egypt |
| 1951.01.27 | Egypt | Apostolic Vicariate of Delta del Nilo was renamed as Apostolic Vicariate of Heliopolis of Egypt |
| 1951.01.27 | Egypt | Apostolic Vicariate of Canal of Suez was renamed as Apostolic Vicariate of Port-Said |
| 1951.01.27 |  Philippines | Diocese of Capiz was established (from Diocese of Jaro and became suffragan of Cebu) |
| 1951.01.27 | Philippines | Territorial Prelature of Ozamiz was established (from Diocese of Cagayan de Oro and Diocese of Zamboanga and became suffragan of Manila) |
| 1951.02.08 |  Bolivia | Apostolic Vicariate of Chaco was renamed as Apostolic Vicariate of Cuevo |
| 1951.02.08 |  Colombia | Apostolic Vicariate of Florencia was established (from Apostolic Vicariate of Caquetá) |
| 1951.02.08 | Colombia | Apostolic Prefecture of Leticia was established (from Apostolic Vicariate of Caquetá) |
| 1951.02.08 | Colombia | Apostolic Vicariate of Caquetá was renamed as Apostolic Vicariate of Sibundoy (lost territory to establish Apostolic Vicariate of Florencia and Apostolic Prefecture of Leticia) |
| 1951.02.08 |  India | Metropolitan Archdiocese of Pondicherry lost territory to Metropolitan Archdiocese of Calcutta and Diocese of Calicut |
| 1951.02.08 |  Indonesia | Apostolic Prefecture of Bangka dan Billiton was promoted as Apostolic Vicariate of Pangkal-Pinang |
| 1951.02.17 |  Canada | Military Vicariate of Canada was established |
| 1951.03.02 | Canada | Diocese of Sherbrooke was promoted as Metropolitan Archdiocese of Sherbrooke (with suffragan sees Nicolet and Saint-Hyacinthe) |
| 1951.03.08 |  Congo-Kinshasa | Apostolic Vicariate of Northern Katanga was renamed as Apostolic Vicariate of Kongolo |
| 1951.03.08 |  Gambia | Mission sui juris of Gambia was promoted as Apostolic Prefecture of Bathurst in Gambia |
| 1951.03.08 | Indonesia | Apostolic Vicariate of Lesser Sunda Islands was renamed as Apostolic Vicariate of Endeh (lost territory to establish Apostolic Vicariate of Larantuka and Apostolic Vicariate of Ruteng) |
| 1951.03.08 | Indonesia | Apostolic Vicariate of Larantuka was established (from Apostolic Vicariate of Lesser Sunda Islands) |
| 1951.03.08 | Indonesia | Apostolic Vicariate of Ruteng was established (from Apostolic Vicariate of Lesser Sunda Islands) |
| 1951.03.08 |  Madagascar | Apostolic Prefecture of Ambanja was promoted as Apostolic Vicariate of Ambanja |
| 1951.03.08 |  Zambia | Apostolic Vicariate of Lwangwa was renamed as Apostolic Vicariate of Abercorn |
| 1951.03.10 |  Brazil | Diocese of Passo Fundo was established (from Diocese of Santa Maria and became suffragan of Porto Alegre) |
| 1951.03.10 | Canada | Apostolic Exarchate of Western Canada (Ukrainian Rite) was renamed as Apostolic Exarchate of Edmonton |
| 1951.03.10 | Canada | Apostolic Exarchate of Central Canada (Ukrainian Rite) was renamed as Apostolic Exarchate of Manitoba (lost territory to establish Apostolic Exarchate of Saskatoon) |
| 1951.03.10 | Canada | Apostolic Exarchate of Saskatoon (Ukrainian Rite) was established (from Apostolic Exarchate of Central Canada) |
| 1951.03.10 | Canada | Apostolic Exarchate of Eastern Canada (Ukrainian Rite) was renamed as Apostolic Exarchate of Toronto |
| 1951.03.10 |  Guatemala | Apostolic Administration of El Petén was established (from Diocese of Vera Paz) |
| 1951.03.10 | Guatemala | Diocese of Jalapa was established (from Metropolitan Archdiocese of Guatemala and became suffragan of Guatemala) |
| 1951.03.10 | Guatemala | Diocese of San Marcos was established (from Diocese of Quetzaltenango, Los Altos and became suffragan of Guatemala) |
| 1951.03.10 | Guatemala | Diocese of Sololá was established (from Metropolitan Archdiocese of Guatemala and Diocese of Quetzaltenango, Los Altos and became suffragan of Guatemala) |
| 1951.03.10 | Guatemala | Diocese of Zacapa was established (from Metropolitan Archdiocese of Guatemala and became suffragan of Guatemala) |
| 1951.03.10 |  USA | Diocese of Greensburg was established (from Diocese of Pittsburgh and became suffragan of Philadelphia) |
| 1951.03.31 | USA | Diocese of Salt Lake was renamed as Diocese of Salt Lake City |
| 1951.04.12 |  Ecuador | Apostolic Vicariate of Méndez y Gualaquiza was renamed as Apostolic Vicariate of Méndez |
| 1951.04.12 |  South Sudan | Apostolic Prefecture of Bahr el-Gebel was promoted as Apostolic Vicariate of Bahr el-Gebel |
| 1951.05.08 |  Italy | Territorial Prelature of Beatissima Vergine Maria del Santissimo Rosario was renamed as Territorial Prelature of Pompei |
| 1951.05.10 |  China | Apostolic Prefecture of Puqi 蒲圻 was promoted as Diocese of Puqi 蒲圻 (became suffragan of Hankou 漢口) |
| 1951.05.10 | China | Apostolic Prefecture of Xiangyang 襄陽 was promoted as Diocese of Xiangyang 襄陽 (became suffragan of Hankou 漢口) |
| 1951.05.10 | China | Apostolic Prefecture of Zhouzhi 盩厔 was promoted as Diocese of Zhouzhi 盩厔 (became suffragan of Xi’an 西安) |
| 1951.05.10 |  Tanzania | Apostolic Prefecture of Dodoma was promoted as Apostolic Vicariate of Dodoma |
| 1951.05.10 |  Uganda | Apostolic Vicariate of Upper Nile was renamed as Apostolic Vicariate of Tororo |
| 1951.05.17 |  Chad | Apostolic Prefecture of Moundou was established (from Apostolic Prefecture of Fort-Lamy and Apostolic Prefecture of Garoua) |
| 1951.05.17 |  Cote d’Ivoire | Apostolic Vicariate of Bouaké was established (from Apostolic Vicariate of Abidjan) |
| 1951.05.17 | South Africa | Military Vicariate of South African Defence Force was established |
| 1951.05.19 | USA | Diocese of Dodge City was established (from Diocese of Wichita and became suffragan of Saint Louis) |
| 1951.06.07 |  Australia | Diocese of Port Augusta was renamed as Diocese of Port Pirie |
| 1951.06.14 | Congo-Kinshasa | Apostolic Prefecture of Isangi was established (from Apostolic Vicariate of Basankusu, Apostolic Vicariate of Coquilhatville, Apostolic Vicariate of Lisala and Apostolic Vicariate of Stanleyville) |
| 1951.06.14 | Congo-Kinshasa | Apostolic Prefecture of Kole was established (from Apostolic Vicariate of Léopoldville and Apostolic Vicariate of Tshumbe) |
| 1951.06.14 | India | Diocese of Sambalpur was established (from Metropolitan Archdiocese of Calcutta, Diocese of Nagpur and Diocese of Ranchi and became suffragan of Calcutta) |
| 1951.06.21 | India | Metropolitan Archdiocese of Agra lost territory to Diocese of Ajmer |
| 1951.06.23 | Canada | Diocese of Saint-Jérôme was established (from Metropolitan Archdiocese of Montréal, Metropolitan Archdiocese of Ottawa and Diocese of Mont-Laurier and became suffragan of Montréal) |
| 1951.06.23 | Canada | Diocese of Sainte-Anne-de-la-Pocatière was established (from Metropolitan Archdiocese of Québec and became suffragan of Québec) |
| 1951.06.23 | USA | Diocese of Juneau was established (from Apostolic Vicariate of Alaska) |
| 1951.06.23 | USA | Diocese of Seattle was promoted as Metropolitan Archdiocese of Seattle (with suffragan sees Spokane and Yakima and lost territory to establish Diocese of Yakima) |
| 1951.06.23 | USA | Diocese of Yakima was established (from Diocese of Seattle and Diocese of Spokane and became suffragan of Seattle) |
| 1951.06.29 |  Mexico | Diocese of Veracruz–Jalapa was promoted as Metropolitan Archdiocese of Veracruz–Jalapa (with suffragan see Papantla) |
| 1951.06.29 | Philippines | Diocese of Nueva Caceres was promoted as Metropolitan Archdiocese of Caceres (with suffragan sees Legazpi and Sorsogon and lost territory to establish Diocese of Legazpi and Diocese of Sorsogon) |
| 1951.06.29 | Philippines | Diocese of Cagayan de Oro was promoted as Metropolitan Archdiocese of Cagayan de Oro (with suffragan sees Surigao, Cotabato and Sulu, Davao and Ozamiz) |
| 1951.06.29 | Philippines | Diocese of Jaro was promoted as Metropolitan Archdiocese of Jaro (with suffragan see Bacolod) |
| 1951.06.29 | Philippines | Diocese of Legazpi was established (from Diocese of Nueva Caceres and became suffragan of Caceres) |
| 1951.06.29 | Philippines | Diocese of Nueva Segovia was promoted as Metropolitan Archdiocese of Nueva Segovia (with suffragan see Batanes and the Babuyan Islands) |
| 1951.06.29 | Philippines | Diocese of Sorsogon was established (from Diocese of Nueva Caceres and became suffragan of Caceres) |
| 1951.07.12 | India | Diocese of Dibrugarh was established (from Diocese of Shillong and became suffragan of Calcutta) |
| 1951.07.12 |  Japan | Apostolic Prefecture of Kyoto 京都 was promoted as Diocese of Kyoto 京都 |
| 1951.07.12 |  Malawi | Apostolic Vicariate of Nyassa was renamed as Apostolic Vicariate of Likuni |
| 1951.07.12 | Philippines | Apostolic Prefecture of Mindoro was promoted as Apostolic Vicariate of Calapan |
| 1951.07.19 |  Guadeloupe,  Saint Barthélemy,  Saint Martin | Diocese of Guadeloupe et Basse-Terre was renamed as Diocese of Basse-Terre et Pointe-à-Pitre |
| 1951.08.01 | Colombia | Territorial Prelature of Bertrania en el Catatumbo was established (from Diocese of Nueva Pamplona and Diocese of Santa Marta and became suffragan of Cartagena) |
| 1951.09.01 | Colombia | Diocese of Zipaquirá was established (from Metropolitan Archdiocese of Bogotá in Colombia and became suffragan of Bogotá in Colombia) |
| 1951.09.10 | Ecuador | Apostolic Vicariate of Los Ríos was promoted as Territorial Prelature of Los Ríos (became suffragan of Quito) |
| 1951.10.18 |  Burkina Faso | Apostolic Vicariate of Bobo-Dioulasso lost territory to Apostolic Vicariate of Nouna |
| 1951.10.18 | Burkina Faso | Apostolic Prefecture of Nouna was promoted as Apostolic Vicariate of Nouna (gained territory from Apostolic Vicariate of Bobo-Dioulasso) |
| 1951.10.31 |  Eritrea | Ordinariate of Eritrea (Eritrean Rite) was promoted as Apostolic Exarchate of Asmara |
| 1951.10.31 |  Ethiopia | Apostolic Vicariate of Addis Abeba was suppressed (to establish Apostolic Exarchate of Addis Abeba) |
| 1951.10.31 | Ethiopia | Apostolic Exarchate of Addis Abeba (Ethiopic Rite) was established (from Apostolic Prefecture of Dessiè, Apostolic Prefecture of Endeber and Apostolic Prefecture of Gondar, from the suppressed Apostolic Vicariate of Addis Abeba and without ecclesiastical province) |
| 1951.11.14 | Brazil | Ordinariate of Ordinariato para os Fiéis de Ritos Orientais no Brasil (Eastern Rite) was established |
| 1951.11.15 | Australia | Diocese of Wollongong was established (from Metropolitan Archdiocese of Sydney and Archdiocese of Canberra and Goulburn and became suffragan of Sydney) |
| 1951.12.13 | Bolivia | Apostolic Vicariate of Ñuflo de Chávez was established (from Apostolic Vicariate of Chiquitos) |
| 1951.12.13 | India | Diocese of Raigarh–Ambikapur was established (from Diocese of Nagpur and Diocese of Ranchi and became suffragan of Calcutta) |
| 1951.12.13 | Tanzania | Apostolic Vicariate of Lower Kagera was established (from Apostolic Vicariate of Bubuka) |
