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 53,917 square kilometres (20,817 sq mi), covering seven provinces of Thailand - Amnat Charoen, Maha Sarakham, Roi Et, Sisaket, Surin, Ubon Ratchathani and Yasothon.

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.