Khian Sa (Thai: เคียนซา, pronounced [kʰīa̯n sāː]) is a district (amphoe) in Surat Thani province, Thailand.

Neighboring districts are (from the north clockwise) Khiri Rat Nikhom, Phunphin, Ban Na Doem, Ban Na San, Wiang Sa, Phrasaeng and Phanom.

Khian Sa is about 60 kilometres from Surat Thani.

The main road through the district is Thailand Route 44, which connects Krabi with Khanom.

[2] The district is divided into five sub-districts (tambons), which in turn are further subdivided into 52 villages (mubans).