The Lake Biwa Mainichi Marathon held in Otsu, Shiga, is one of the prominent Japanese marathon races of the year. It is a male-only competition and has IAAF Gold Label status. It was first held in 1946 and, having taken place every year since then, it is Japan's oldest annual marathon race. The early editions of the race were held in Osaka until a switch to Tokyo occurred for the 1963–65 marathons, and all subsequent races thereafter were held in Otsu, near Lake Biwa, where the race gets its name. It is sponsored by Mainichi.

The race begins and ends at the Ojiyama Stadium. The Lake Biwa Marathon has been selected as the Japanese national marathon championships on dozens of occasions, starting in 1960. The current course record for the competition is 2:06:13 set by Wilson Kipsang at the 2011 edition.