| Date | Country | Change |
| 1918 | Apostolic Vicariate of Kimberley in Orange was renamed as Apostolic Vicariate of Kimberley in South Africa | |
| 1918.01.11 | Diocese of Lafayette in Louisiana was established (from Metropolitan Archdiocese of New Orleans and became suffragan of New Orleans) | |
| 1918.01.17 | Diocese of Leiria was restored (from Patriarchal See of Lisboa and Diocese of Coimbra and became suffragan of Lisboa) | |
| 1918.03.13 | Apostolic Prefecture of Dutch Borneo was promoted as Apostolic Vicariate of Dutch Borneo | |
| 1918.03.14 | Apostolic Prefecture of Urabá was established | |
| 1918.07.18 | Diocese of Aterrado was established (from Metropolitan Archdiocese of Mariana and Diocese of Uberaba and became suffragan of Mariana) | |
| 1918.07.26 | Metropolitan Archdiocese of Olinda was renamed as Metropolitan Archdiocese of Olinda e Recife | |
| 1918.08.02 | Diocese of Floresta was suppressed (to establish Diocese of Pesqueira) | |
| 1918.08.02 | Diocese of Garanhuns was established (from Metropolitan Archdiocese of Olinda e Recife and became suffragan of Olinda e Recife) | |
| 1918.08.02 | Diocese of Nazaré was established (from Metropolitan Archdiocese of Olinda e Recife and became suffragan of Olinda e Recife) | |
| 1918.08.02 | Diocese of Pesqueira was established (from Metropolitan Archdiocese of Olinda e Recife, from the suppressed Diocese of Floresta and became suffragan of Olinda e Recife) | |
| 1918.08.24 | Apostolic Prefecture of Betafó was promoted as Apostolic Vicariate of Betafó | |
| 1918.08.24 | Apostolic Prefecture of Western Nigeria was promoted as Apostolic Vicariate of Western Nigeria | |
| 1918.09.22 | Diocese of Riga was restored (from Metropolitan Archdiocese of Mohilev) |
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