Nishikawa Castle, Castle ruin in Toyohashi, Japan.

Nishikawa Castle is a castle ruin in Toyohashi with earthen ramparts and a dry moat situated on elevated ground. The site lies in Aichi Prefecture in central Japan and retains the outlines of its former defensive layout.

Saigo Kiyokazu built Nishikawa Castle between 1532 and 1555 as a branch castle of the Saigo clan, whose headquarters was Wachigaya Castle. The Mikawa Chorography of 1740 records that it was raised against the rival Makino clan of neighbouring Toyokawa. In 1590 Saigo Iekazu was moved to Oyumi Castle and custody passed to the Ogasawara; the castle was abandoned in 1661.

The site reflects the defensive role that such structures played during Japan's feudal period. Visitors can still see how the elevated position and layout controlled the surrounding terrain.

Visitors can explore the remaining ramparts and castle grounds by following marked paths that wind through the site. The terrain is easy to walk and provides good views of how the fortification was once laid out.

The name Nishikawa was coined as a pledge of allegiance to the Imagawa: it joins the first kanji of Saigo (西) with the second kanji of Imagawa (川). The Saigo kept their headquarters at Wachigaya Castle, so this hilltop post was a branch stronghold facing the Makino of neighbouring Toyokawa.