Mukdahan (also Mukdaharn) is one of the north-eastern provinces of Thailand. Neighboring provinces are (from south clockwise) Amnat Charoen, Yasothon, Roi Et, Kalasin, Sakon Nakhon and Nakhon Phanom. To the east it borders the Mekong River, across which lies Savannakhet Province of Laos.
The province is located in the Mekong valley. In the west of the province are the Phu Phan mountains, which are covered with thick forests.
Mukdahan became Thailand's 73d province in 1982. Located in the northeastern (Isan) region of the country, on the banks of the river Mekong, it was formerly as district of Nakhon Phanom Province.