The "JAPAN ULTRA-MARATHON CHALLENGE SERIES" is a series of ultra-marathon races in Japan. This project was started to support runners who take on challenges, as well as spread the attractiveness of ultra-marathon.

The series consists of four leading races being held all across Japan: The Shimanto River Ultra-marathon (October), The Okinawa 100K Ultra-marathon (December), The Shibamata 100K (May), and The Lake Saroma 100km Ultra Marathon (June).

The organizer gives the title of "Ultra Maestro" and exclusive items to runners who complete all four races in two years.

JAPAN ULTRA-MARATHON CHALLENGE SERIES Official Website (Japanese only): https://runnet.jp/project/jucs

* Official website of each race
・ Shimanto River Ultra-marathon: http://shimanto-ultra.jp/
・ Okinawa 100K Ultra-marathon: http://www.okinawa100k.jp/
・ Shibamata 100K: https://tokyo100k.jp/
・ Saroma Lake 100km Ultra Marathon: http://saromanblue.jp/