Karatsu, city, northwestern Saga ken (prefecture), northwestern Kyushu, Japan. It is located on Karatsu Bay, about 30 miles (50 km) southwest of Fukuoka.
The city’s name is derived from the Japanese terms kara (referring to China) and tsu (“port”), reflecting the city’s history as an ancient port trading with China and Korea. The Karatsu coal mines operated through much of the 20th century, and after World War II the western part of the city developed as an industrial district, centring on the fishing harbour. Manufactures include chemicals and ceramics. The eastern part of Karatsu—rich in historic sites and scenic beauty—serves as a tourist centre for Genkai Quasi-national Park. Pop. (2005) 131,116; (2010) 126,926.