However, in the period of Nagatoki, the eldest son of Nagamune, it was defeated by Shingen TAKEDA from Kai who was aiming to territorialize Shinano, at the Battle of Shiojiritoge, and Nagatoki was exiled from Shinano and the Fuchu-Ogasawara clan went to ruin.
しかし、長棟の長男の長時の時代になると塩尻峠の戦いで信濃の領国化を目指す甲斐の武田信玄に大敗し、長時は信濃から追われて府中小笠原氏は滅亡する。