Nan is one of the northern provinces of Thailand. Neighboring provinces are (from south clockwise) Uttaradit, Phrae and Phayao. To the north and east it borders Xaignabouli of Laos.
The province is located in the remote valley of the Nan River, surrounded by mountains covered with forests. The highest mountain is the 2079 meter high Doi Phu Kha in Amphoe Pua, north-east of the city of Nan towards the border with Laos.