Sain Qaleh (Persian: صائين قلعه)[a] is a city in the Central District of Abhar County, Zanjan province, Iran.

Originally in the former Khorramdarreh District[4] before its separation from the county to establish Khorramdarreh County, Sain Qaleh was transferred to the Central District.

[5] At the time of the 2006 National Census, the city's population was 11,083 in 2,896 households.

[7] The 2016 census measured the population of the city as 12,989 people in 4,048 households.

[2] The 14th-century author Hamdallah Mustawfi mentioned Sa'in Qal'eh in his Nuzhat al-Qulub: he referred to "the village called Quhūd, which the Mongols call Sāin Qal'ah, and which is the chief of all those neighboring hamlets".