Sai Noi is the northwesternmost district (amphoe) of Nonthaburi Province, central Thailand. Neighboring districts are Lat Bua Luang (Ayutthaya Province); Lat Lum Kaeo (Pathum Thani Province); Bang Bua Thong, Bang Yai, and the districts Phutthamonthon and Bang Len of Nakhon Pathom Province.
