Rat Niyom (, ) is one of the seven subdistricts (tambon) of Sai Noi District, in Nonthaburi Province, Thailand. The subdistrict is bounded by (clockwise from north) Sam Mueang, Bo Ngoen, Namai, Lahan, Khlong Khwang, Khun Si and Sai Yai subdistricts. In 2020 it had a total population of 6,759 people.
The subdistrict is subdivided into 8 administrative villages (muban).
The whole area of the subdistrict is covered by Rat Niyom Subdistrict Administrative Organization ().