The Kok River flows in Southeast Asia. The river originates in the Daen Lao Range, Shan State, Burma. It flows southeastwards across the Burma-Thailand border to Mae Ai district, Chiang Mai Province. Most of its length in Thailand is in Chiang Rai Province where it passes Mueang Chiang Rai District after which it bends northeastwards and flows through Mae Chan, Wiang Chai and Chiang Saen districts. The Kok River is a tributary of the Mekong River, with its mouth at Sop Kok in Chiang Saen district, opposite the Lao border. Phahonyothin Road crosses this river near Chiang Rai City.
The main tributaries of the Kok River are the Fang and the Lao River, the latter having its source in the Phi Pan Nam Range.