The Mae Klong (Thai: แม่น้ำแม่กลอง, RTGS: Maenam Mae Klong, ) is a river in western Thailand. The river begins at the confluence of the Khwae Noi or Khwae Sai Yok and the Khwae Yai River or Khwae Si Sawat in Kanchanaburi, passes Ratchaburi Province and empties into the Gulf of Thailand in Samut Songkhram.
In the 1960s the upper stretch of the river until the town of Kanchanaburi was renamed to Khwae Yai (แควใหญ่, big tributary), as the famous Bridge on the River Kwai spanned the Mae Klong and not the Khwae (Kwai) river. However the actual origin of the river is in the Tenasserim Hills, around the Khuean Srinagarindra National Park area in the north of Kanchanaburi Province.
Note that an early portion of Khwae Yai River in Amphoe Umphang, Tak Province is also called Klong River. It becomes known as Khwae Yai River when it flows into Kanchanaburi Province.
It feeds the giant Umphang Thee Lor Sue Waterfall in its upper reaches.
Giant freshwater stingrays are often caught in the Mae Klong River.