Mount Kōtsu, Mountain summit in Yoshinogawa, Japan

Mount Kōtsu is a 1133-meter peak at the northern end of the Tsurugi Mountains, facing the Yoshino River plain; its summit area belongs to Yoshinogawa, Tokushima Prefecture. The mountain rises about 1000 meters above the plain and presents a neat triangular profile from the north. A first-order triangulation point stands on the summit, and the highest point lies about 100 meters south of it.

Kōtsu-ji, the temple at the summit, was founded in the 7th century by the ascetic En no Ozunu, according to temple tradition. In the Enryaku era (782–802) Kūkai is said to have carved the temple's main image and buried a copy of the Lotus Sutra on the peak. By 1361 the temple held estates in the plain, and in the Edo period it became a temple of Daikaku-ji in Kyoto.

The name Kōtsu is said to come from the legend that Zaō Gongen flew over the mountains from Yoshino to this peak. Locals also call it Awa Fuji and, affectionately, Okōtsu-san. On the 18th day of the eighth lunar month, yamabushi in mountain ascetic dress gather at Kōtsu-ji for the Jūhachi Yamakai rite with its purple-light goma fire.

Well-marked trailheads with parking areas are distributed around the mountain and easy to locate. Nearby towns offer places to stay and supply stops for provisions before heading up.

The eclogite found on the mountain's eastern foot, called Kōtsu eclogite, formed at pressures of about 1.4 to 2.5 GPa, roughly 40 to 75 km underground, at around 600 °C. Such eclogite-facies rock in the Sanbagawa belt is otherwise known in Japan only near Mount Higashi-Akaishi.