Date | Country | Change |
| 2018.01 |  Italy | Titular Episcopal See of Bisenzio was restored |
| 2018.01 | Italy | Titular Episcopal See of Milazzo was restored |
| 2018.01 | Italy | Titular Episcopal See of Rosella was restored |
| 2018.01 |  Spain | Titular Episcopal See of Ampurias was restored |
| 2018.01 | Spain | Titular Episcopal See of Armentia was restored |
| 2018.01 | Spain | Titular Episcopal See of Valpuesta was restored |
| 2018.01.23 |  USA | Diocese of Winona was renamed as Diocese of Winona–Rochester |
| 2018.02.28 |  Nigeria,  Angola,  Benin,  Burkina Faso,  Cameroon,  Central African Republic,  Chad,  Congo-Brazzaville,  Congo-Kinshasa,  Cote d’Ivoire,  Equatorial Guinea,  Gabon,  Gambia,  Ghana,  Guinea,  Guinea-Bissau,  Liberia,  Mali,  Mauritania,  Niger,  Senegal,  Sierra Leone,  Togo | Apostolic Exarchate of Western and Central Africa (Maronite Rite) was promoted as Diocese of Annunciation of Ibadan (without ecclesiastical province) |
| 2018.03 | Italy | Titular Episcopal See of Alesa was restored |
| 2018.03.01 |  Saint Pierre and Miquelon | Apostolic Vicariate of Îles Saint-Pierre et Miquelon was suppressed (to Diocese of La Rochelle) |
| 2018.04.25 |  Thailand | Diocese of Chiang Rai was established (from Diocese of Chiang Mai and became suffragan of Bangkok) |
| 2018.05.20 | USA | Diocese of Fargo lost territory to Diocese of Bismarck |
| 2018.05.31 |  North Macedonia | Apostolic Exarchate of Macedonia (Macedonian Rite) was promoted as Diocese of Assumption of the Blessed Virgin Mary in Strumica–Skopje (without ecclesiastical province) |
| 2018.05.31 |  Venezuela | Diocese of El Tigre was established (from Diocese of Barcelona and became suffragan of Cumaná) |
| 2018.06.29 | Italy | Patriarchal See of Venezia lost territory to Diocese of Concordia–Pordenone |
| 2018.09.05 |  Kosovo | Apostolic Administration of Prizren was promoted as Diocese of Prizren–Prishtina (without ecclesiastical province) |
| 2018.09.08 |  China | Diocese of Chengde 承德 was established (from Diocese of Chifeng 赤峰 and Diocese of Rehe 熱河 and became suffragan of Beijing 北京) |
| 2018.10.31 | North Macedonia | Titular Episcopal See of Strumnitza was suppressed (to Diocese of Assumption of the Blessed Virgin Mary in Strumica–Skopje) |
| 2018.12.03 |  Canada | Diocese of Hearst was renamed as Diocese of Hearst–Moosonee (gained territory from the suppressed Diocese of Moosonee) |
| 2018.12.03 | Canada | Diocese of Moosonee was suppressed (to Diocese of Hearst–Moosonee) |
| 2018.12.06 |  Serbia, Kosovo | Apostolic Exarchate of Serbia (Croatian Rite) was promoted as Diocese of Saint Nicholas of Ruski Krstur (without ecclesiastical province) |
| 2018.12.21 |  Tanzania | Diocese of Mbeya was promoted as Metropolitan Archdiocese of Mbeya (with suffragan sees Iringa and Sumbawanga) |
| 2018.12.22 | Canada | Apostolic Exarchate of Canada (Syro-Malabar Rite) was promoted as Diocese of Mississauga (without ecclesiastical province) |
| 2018.12.22 |  Iraq | Diocese of Aqrā (Chaldean Rite) was suppressed (to Archdiocese of Mossul–Aqrā) |
| 2018.12.22 | Iraq | Archdiocese of Mossul (Chaldean Rite) was renamed as Archdiocese of Mossul–Aqrā (gained territory from the suppressed Diocese of Aqrā) |
| 2018.12.22 |  Vietnam | Diocese of Hà Tĩnh was established (from Diocese of Vinh and became suffragan of Hà Nôi) |
| 2018.12.28 |  Bangladesh | Diocese of Barisal was renamed as Diocese of Barishal |
| 2018.12.28 | Bangladesh | Metropolitan Archdiocese of Chittagong was renamed as Metropolitan Archdiocese of Chattogram |
