Distance
Climb
Start Time
Cutoff
Terrain
The OSJ KOUMI100 is a 168.33 km solo mountain ultra that sets off from Koumi Town in Nagano Prefecture at 07:00 on 11 October 2026. Runners climb and descend close to 8,000 m across the course, supported by five aid stations, and have 36 hours to reach the finish. Entry is capped at 500 participants and the race forms part of the OSJ Trail Running Race Series. The ITRA listing grades it at Mountain Level 6 with a Finisher Level of 10, a sign of how sustained the climbing and descending are.
168.33 km loop through the mountains around Koumi Town
7,916 m of cumulative climbing
Part of the OSJ Trail Running Race Series
Start / Finish
Koumi Town, Nagano Prefecture, Japan
Koumi Town, Nagano Prefecture, Japan
Getting There
Race Day
On the day
Before you enter
Other questions
The race is held on 11 October 2026, starting at 07:00 local time from Koumi Town in Nagano Prefecture, Japan.
The course is rated at ITRA Mountain Level 6 and Finisher Level 10, which places it firmly in the experienced mountain ultra bracket. Prospective entrants should have a solid background in long trail races and night running.
Yes. The Koumi 100 is a counting race in the OSJ Trail Running Race Series, the Japanese trail series run by OSJ.
Early October in the Nagano mountains brings cool mornings and mild days, with temperatures dropping sharply at altitude and after dark. Runners should prepare for cold, wet conditions on the high sections and carry layers accordingly.
With a 36 hour limit from a 07:00 start, most of the field will spend at least one night on the course. A reliable head torch and spare batteries are essential.
Entry fee
Registration isn't open yet. We'll show pricing when the organiser confirms.Koumi, Japan
Expected October 2027
Provisional date, around Oct 10Are you the organiser of OSJ KOUMI100 2027 - 100 Miles?
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