In 1455, internal strife within the Chiba clan, the head family of the To clan, broke out in Shimotsuke Province, and as ordered by Yoshimasa ASHIKAGA, the Barbarian-subduing General, Tsuneyori supported the bereaved children of Tanekata Chiba, Sanetaka and Yoritaka, and fought in the Kanto area.
1455年（康正元年）下総国で起きた本家にあたる千葉氏の内紛を収めるため、征夷大将軍足利義政の命により、嫡流の千葉胤賢の遺児千葉実胤と千葉自胤を支援し関東を転戦した。