In the Kamakura period the clan was an estate steward of six counties in Gohoku, and the original forefather Ujinobu SASAKI became The High Court of Justice of the Kamakura bakufu (Japanese feudal government headed by a shogun), and Munetsuna SASAKI who inherited Ujinobu, worked as an envoy at the time when the bakufu prompted the Imperial Court to pass the throne to the successor.
鎌倉時代は江北六郡の地頭であり、始祖の佐々木氏信は鎌倉幕府の評定衆を務め、後を継いだ佐々木宗綱は、幕府が朝廷に対し天皇の譲位を促した際の使者を務めている。