| Jurisdiction: | Diocese |
| Ubon Ratchathani | |
| Latin: | Dioecesis Ubonratchathaniensis |
| Local: | Thai: สังฆมณฑลอุบลราชธานี |
| Country: |  Thailand |
| Province: | Thare and Nonseng |
| Metropolitan: | Thare and Nonseng |
| Area Km2: | 53,917 |
| Population: | 7,785,113 |
| Population As Of: | 2010 |
| Catholics: | 26,242 |
| Catholics Percent: | 0.3 |
| Denomination: | Catholic |
| Sui Iuris Church: | Latin Church |
| Rite: | Roman Rite |
| Cathedral: | Cathedral of the Immaculate Conception in Ubon Ratchathani |
| Bishop Title: | Bishop elect |
| Bishop: | Stephen Boonlert Phromsena |
| Metro Archbishop: | Anthony Weradet Chaiseri |
| Emeritus Bishops: | Philip Banchong Chaiyara |
| Map: | Thailand Diocese Ubon Ratchathani.png |
The Roman Catholic Diocese of Ubon Ratchathani (Dioecesis Ubonratchathaniensis, Thai: สังฆมณฑลอุบลราชธานี) is located in north-east Thailand. It is a suffragan diocese of the archdiocese of Thare and Nonseng.
The diocese covers an area of, covering seven provinces of Thailand - Amnat Charoen, Maha Sarakham, Roi Et, Sisaket, Surin, Ubon Ratchathani and Yasothon. In 2001, of the 7.7 million citizens, 24,760 were members of the Catholic Church. It is divided into 55 parishes, with 42 priests altogether.
The Vicariate Apostolic of Ubon was created on May 7, 1953, when the Vicariate Apostolic of Thare was split. In 1965, the western part of the territory was separated and became the Vicariate Apostolic of Nakhon Ratchasima. On December 18, 1965, the Vicariate Apostolic was elevated to a diocese.
The cathedral of the diocese is the Cathedral of the Immaculate Conception, located in Ubon Ratchathani.
May 21, 1976 - March 25, 2006 (retired)