Komoro Castle (小諸城 Komoro-jō?) is a hirayamashiro (hilltop castle) located in Komoro, Nagano Prefecture, Japan. The castle was constructed in 1554 by Takeda Shingen. In 1590, Sengoku Hidehisa became the lord. He was followed by his son, Sengoku Tadamasa. Tadamasa improved the castle, and the tenshu (keep)'s foundation dates from this time. The tenshu itself burned down during the Edo Period. Much of what remained of the castle was demolished in 1871, during the Meiji Restoration.
Currently, the castle's ruins are open to the public, along with two gates, the Ōtemon and Sannomon, both of which have been declared Important Cultural Properties. Also located in the castle is an amusement park, a zoo which opened in 1926, and a museum dedicated to Shimazaki Toson.