The Phum Duang River or Maenam Phum Duang is a river in Surat Thani Province, southern Thailand, the main tributary of the Tapi River. The river drains an area of 6,125 square kilometres (2,365 sq mi) west of the Tapi watershed, mainly the eastern slopes of the Phuket mountain range. It joins the estuary of the Tapi 5 kilometres (3 mi) west of Surat Thani in Phunphin District. The river flows through the districts of Phanom, Ban Ta Khun, Khiri Rat and Phunphin.