Gyaing River^[1] (Burmese: ဂျိုင်းမြစ်) is a river of Kayin State and Mon State, in southeastern Burma (Myanmar). Its two major tributaries, the Hlaingbwe River and the Haungtharaw River, flow together to form the Gyaing^[2] at 16°36′12″N 98°00′25″E.^[3] It is about 45 miles (72 km) long^[2] and flows into the Salween River immediately above Moulmein, at 16°30′55″N 97°37′36″E (its mouth).^[3]

The Gyaing is a wide river, but quite shallow with numerous sandbars.^[2] It is navigable by smaller boats all year long.^[2] Important towns and villages along its banks include Gadoe (Kado), Zathabyin (Zathabyeng),^[4] Kalagong, Kawbein, Peinnegon,^[5] Tarana^[6] and Damathat (Dhammatha). The up-stream Gyaing forms part of the border between Hpa-an District and Kawkareik District of Kayin State, and downstream is the border between Kayin State and Mon State.^[1]