Yamaga (山鹿市, Yamaga-shi) is a city in Kumamoto Prefecture, Japan.

There are many burial mounds dating from the Kofun period within the city limitsm and the name "Yamaga" appears in early 8th century records.

During the Kamakura period, the area developed as a hot spring town and in the Muromachi period it developed into a commercial settlement and a post town on the Buzen Kaido highway, and was noted for its production of umbrellas.

After the Meiji restoration, the town of Yamaga was established with the creation of the modern municipalities system on April 1, 1889.

Yamaga has a mayor-council form of government with a directly elected mayor and a unicameral city council of 20 members.

In terms of national politics, the city is part of the Kumamoto 3rd district of the lower house of the Diet of Japan.