The Battle of Namanoyama occurred on 11/27 of Eiroku 4 (1561) at Namanoyama in the Yokomi District of Musashi Province during the Sengoku period.  The conflict was waged between Hōjō Ujiyasu and Uesugi Masatora (later known as Uesugi Kenshin).

In the background of this battle was conflict between the Hōjō and Uesugi clans for control of Matsuyama Castle in a strategic location to pin-down Nakahara in Musashi Province.  After halting an attack by Masatora during the Siege of Odawara Castle, Ujiyasu launched a counterattack to reclaim the northern portion of Musashi which had earlier been seized by the Uesugi so he headed-out to capture Matsuyama Castle and Chichibu-Takamatsu Castle.

Meanwhile, after enduring four episodes of the Battle of Kawanakajima against Takeda Shingen of Kai Province, as soon as Masatora returned to Echigo Province, he dispatched reinforcements.  Whether Masatora himself led this Uesugi army is uncertain.  The Hōjō army intercepted the rear guard of the Uesugi army at Namanoyama close to Matsuyama Castle, triggering a field battle.  In the end, the Hōjō army prevailed.  The Uesugi army withdrew in the direction of Shimotsuke Province and, thereafter, proceeded toward Karasawayama Castle.  The Hōjō army then marched to the provincial border of Kōzuke and Musashi, forcing the surrender of Chichibu-Takamatsu Castle and restoring the sphere of influence of the Fujita clan.  The Hōjō, however, did not advance as far as Matsuyama Castle.  Later, Ujiyasu entered into an alliance with Shingen while Masatora allied with Satomi Yoshitaka in the midst of the ongoing fierce contests for hegemony of the Kantō.