Uesugi Tomosada (上杉朝定, fl. mid-16th century) was a member of the Ōgigayatsu-Uesugi clan (扇谷上杉氏), a branch of the powerful Uesugi clan that held significant influence in the Kantō region of Japan during the Sengoku period (15th-17th centuries). He is primarily known for being the final head of the Ōgigayatsu-Uesugi family and for his resistance against the growing power of the Hōjō clan.
Tomosada inherited a weakened clan, facing constant pressure from the Later Hōjō clan (後北条氏) under Hōjō Ujiyasu. He attempted to maintain control over his territory, primarily centered in Musashi Province, but his efforts were largely unsuccessful.
His main historical significance lies in his participation in the conflicts against the Hōjō. He formed alliances with other anti-Hōjō forces, including the Uesugi Kenshin (長尾景虎, later Uesugi Kenshin) of the Yamanouchi-Uesugi clan. However, these alliances were often fragile and unable to effectively counter the Hōjō's military strength.
In 1546, Tomosada faced a decisive defeat at the Battle of Kawagoe Castle (河越夜戦). This battle, a stunning victory for the Hōjō, effectively shattered the power of the Ōgigayatsu-Uesugi clan. Tomosada himself was killed in battle or shortly thereafter, although the exact circumstances of his death remain debated. His death marked the end of the Ōgigayatsu-Uesugi line as a significant political force in the Kantō region, paving the way for the Hōjō to consolidate their control over the area.
While not a particularly successful leader, Uesugi Tomosada is remembered as a figure who resisted the expansion of the Hōjō clan and represents the decline of the once-powerful Uesugi families during the tumultuous Sengoku period.