Otsu is a city located in Shiga Prefecture, Japan. It is the capital of Shiga Prefecture. Otsu occupies the south-central area of Shiga Prefecture. The city was founded on April 1, 1889. Otsu has a population of 421,849 (as of October 1, 2016) and a population density of 2,500 persons per km². The city is administratively divided into 15 wards.
Lake Biwa, Japan's largest lake, is located partly in Otsu. The lake and the city have provided a backdrop for many famous writers and artists, including Izumi Kyoka and Hokusai. Otsu is also the birthplace of the manga artist Naoko Takeuchi.