Sai Yok (Thai: ไทรโยค, pronounced [sāj jôːk]) is a district (amphoe) in Kanchanaburi province in western Thailand.

Along the river the Death Railway runs to Nam Tok Sai Yok Noi.

Sai Yok National Park was created on 27 October 1980 and covers an area of about 500 km2.

Apart from the nature of the Kwae Noi River valley, the other main attraction is Mueang Sing Historical Park, which shows the westernmost Khmer-style temple complex.

Sai Yok is divided into seven sub-districts (tambons), which are further subdivided into 57 administrative villages (mubans).