Su-ngai Kolok (Thai: สุไหงโกลก, Malay: Sungai Golok) is a border town, subdistrict, and district on the Malaysia-Thailand Border in Narathiwat Province, Thailand. It is one of the largest and most prosperous districts in Narathiwat Province. It is also one of the major economic centers in the southern part of Thailand. It is capital of the Su-ngai Kolok District. As of 2005, the town (thesaban mueang) had a population of 38,612. Across the border is Rantau Panjang, Kelantan, Malaysia.