The average elevation of the province is 580 m. The north of the province belongs to the so-called Golden Triangle, at which the borders of Thailand, Laos and Myanmar converge - an area which was very unsafe because of the drug smuggling across the borders. The Mekong river forms the boundary with Laos, the Mae Sai and Ruak River to Myanmar. Through the town of Chiang Rai itself flows the Kok River.
While the eastern part of the province is relatively flat river plains, the western part consists of the mountainous terrain of the Hills of Northern Thailand.
While not the highest elevation of the province, the 1389 m high Doi Tung (Flag hill) is the most important hill. The Wat Phra That Doi Tung temple on top of the hill according to the chronicles dates back to the year 911. Nearby is the Doi Tung royal villa, former residence of the Late Princess mother (mother of the present king) Somdej Phra Srinagarindra. Thanks to her activities the hills were reforested, and the hill tribes changed from growing poppy to other crops.