Udon Thani (Thai: อุดรธานี, pronounced [ʔudɔːn tʰaːniː]) is one of the four major cities of Isan, Thailand - also known as "Big 4 of Isan". and the capital of Udon Thani Province.

47 km east of Udon Thani is Thailand's premier Bronze Age excavation at Ban Chiang, the world-renowned archaeological site.

Although there are few attractions in the city for most travellers, there are a few interesting Buddhist temples. Within a few kilometers of Udon Thani is Wat Pa Baan That, which was home for many years to Forest Meditation monk Luangta Maha Bua, known for his philanthropic endeavors such as accumulating gold and giving it to the National Treasury to benefit Thailand's citizens during the economic crisis of the late 1990s. It is said that over the course of his tenure at this temple over $550 million (USD) was collected for the benefit of Thai citizens, be it directly or via building of hospitals and clinics. Ajahn Maha Bua died in January 2011.

The city became a bustling support center for the nearby Udorn Royal Thai Air Force Base during the Vietnam War and so retains reminders of that time, with bars coffee shops and hotels.

In the mid-1900s, about 46,700 Vietnamese war refugees immigrated to Udon Thani. Their descendants still reside in Udon Thani and communicate with each other in Vietnamese.[1] Today, Udon Thani has the largest Vietnamese community in all of Thailand.

It also became the site of a Voice of America relay station alleged to have been a CIA black site.

Asia Pacific Resources, a wholly owned subsidiary of Italian-Thai Development PLC, owns the concession to the Udon Thani potash mines and plans to develop them. According to press reports, Udon Thani has enough potash to mine two million tonnes per year for 25 years. Potash is one of the main components in fertilizer.

Udon Thani has a tropical savanna climate (Köppen climate classification Aw). Winters are fairly dry and very warm. Temperatures rise until April, which is hot with the average daily maximum at 36.3 °C (97.3 °F). The monsoon season runs from late April through early October, with heavy rain and somewhat cooler temperatures during the day, although nights remain warm. The range of reliably recorded temperatures in the city is from 2.5 °C (36.5 °F) to 43.9 °C (111.0 °F).