Izumiōtsu, city, western Ōsaka fu (urban prefecture), west-central Honshu, Japan. It is situated on the eastern shore of Ōsaka Bay, southwest of Ōsaka.
An important port since the 8th century, it became a centre of cotton textile production during the Edo (Tokugawa) period (1603–1867). Izumiōtsu lost much of its function as a port town after the Meiji Restoration (1868). Its industry has since shifted to the production of woolen and cotton blankets. The city now produces most of Japan’s cotton blankets, for both domestic use and export. Pop. (2010) 77,548; (2015) 75,897.