Ubon Ratchathani (Thai: อุบลราชธานี, pronounced [ʔù.bōn râːt.t͡ɕʰā.tʰāː.nīː]), often shortened to Ubon (อุบลฯ), is one of Thailand's seventy-six provinces lies in lower northeastern Thailand also called Isan. Ubon is about 630 km (390 mi) from Bangkok. Neighboring Provinces are (from west clockwise) Sisaket, Yasothon, and Amnat Charoen. To the north and east it borders Salavan and Champasak of Laos, to the south Preah Vihear of Cambodia.
The city was founded in the late-18th century by Thao Kham Phong, descendant of Phra Wo and Phra Ta, who escaped from King Siribunsan of Vientiane into Siam Kingdom during the reign of King Taksin the Great. Later Thao Kham Phong was appointed to be "Phra Pathum Wongsa", the first ruler of Ubon Ratchathani. In 1792 Ubon Ratchathani became a province, and was also the administrative center of the monthon Isan. In 1925 it became part of monthon Nakhon Ratchasima. With the abolition of the monthon system in 1933, the province became a first level subdivision of the country. Until 1972, Ubon Ratchathani Province was the largest province of Thailand by area. Yasothon Province was split off from Ubon Ratchathani Province in 1972, followed by Amnat Charoen Province in 1993.