The siege of Iwamura was a military event which occurred in 1572 in Japan, concurrent with Takeda Shingen's push into Tōtōmi Province and the Battle of Mikatagahara.

Akiyama Nobutomo, one of Shingen's "Twenty-Four Generals," set his eye on the great yamashiro (mountain castle) of Iwamura when Tōyama Kagetō, the commander of the castle's garrison, fell ill and died.

[1] Akiyama negotiated the castle's surrender with Lady Otsuya, who was not only Tōyama's widow but the aunt of Oda Nobunaga.

The heir to the castle was a four-year-old boy called Gobōmaru, the fifth son of Oda Nobunaga, who had been given to Tōyama to adopt and raise as his own.

This caused the Takeda-Oda relationship to decline and Nobunaga started a campaign against the Takeda clan.