Onsen-ji, Buddhist temple in Toyooka, Japan.

Onsen-ji is a Shingon Buddhist temple on Mount Daishi above Kinosaki Onsen in Toyooka, Hyogo Prefecture. Its main hall, built around 1387 in the early Muromachi period, is the oldest wooden building in Tajima and an Important Cultural Property. The hall mixes Japanese, Zen and Great Buddha styles and enshrines an Eleven-Faced Kannon. A 450-step stone stairway climbs from the foot of the mountain.

The temple was founded in 738 and gained prominence after a priest named Douchi Shonin discovered the natural hot springs in the surrounding area. This discovery linked the temple directly to the development of Kinosaki as a destination for bathing.

The temple is the guardian shrine of Kinosaki Onsen and belongs to the Koyasan Shingon sect as a special head temple. Its name and mountain name, Matsudai-san, were granted by Emperor Shomu in 738. On April 23 and 24, the Kaizan-ki memorial service for the founder is held. The temple is the 29th stop on the Saigoku Yakushi 49 sacred sites and the 33rd on the Tajima Saigoku 33 Kannon pilgrimage.

From JR Kinosaki Onsen Station the temple is a 15-minute walk; a bus to the "Kono-yu" stop leaves about 2 minutes on foot to the foot of Mt. Daishi. From there 450 stone steps climb to the main hall, or the Kinosaki Onsen ropeway reaches the Onsen-ji station in 3 minutes with the hall just steps away.

The temple's precinct holds a Kani-zuka, a mound for crabs, reflecting the town's long ties to crab fishing. The 450 stone steps of the approach are lined with old trees designated a natural monument by the city. The main hall, built around 1387, is the oldest wooden building in Tajima.