Saika Castle, Japanese castle in Wakayama, Japan.

Saika Castle was a hilltop castle in the Saika district of Wakayama, built by Suzuki Shigeyoshi (Sadayu) on the northern side of the hill where the Myōken-dō stands, on a terrace called Senjōjiki. No clear baileys remain and the old castle site shows almost no trace of its former appearance. At the foot of Myōken-yama are Yōju-ji temple and Jōsekiyama Park (Tsuya Park) at the entrance to the castle hill.

The castle was founded by Suzuki Sadayu during the Sengoku period and served as a stronghold for the Saika Ikki group. It was besieged by Oda Nobunaga in 1577, marking a turning point in regional power.

The castle was the center of a community of craftsmen and warriors who specialized in making firearms. Visitors can still sense the connection between this place and that special craft tradition.

The site has no clearly defined baileys and little remains of the old castle. From Wakayama Station or Nankai Wakayamashi Station take a Wakayama bus to Wakaura-guchi stop, then walk about five minutes. There is no parking nearby; the entrance to the castle hill is at Jōsekiyama Park (Tsuya Park).

Near the castle stood foundries where the Saika Ikki manufactured firearms such as the arquebus. This made the site an important center of weapons production in feudal Japan.