Yamaga (山鹿市, Yamaga-shi) is a city in Kumamoto Prefecture, Japan. As of 31 July 2024, the city had an estimated population of 48,181 in 21996 households, and a population density of 160 persons per km. The total area of the city is 299.69 km (115.71 sq mi).

Yamaga is located in the northern inland area of Kumamoto Prefecture, about 30 kilometers north of Kumamoto City. The city borders Fukuoka Prefecture from the north to the northeast, and Oita Prefecture to the east. The area from the urban center, which is slightly south of the geographic center, to the southern part (former Kikuka Town) is a basin. The northern to northeastern part of the city near the prefectural border is part of the Kyushu Mountains. The Kikuchi River flows through the center of the city.

Fukuoka Prefecture

• Yame

Kumamoto Prefecture

• Gyokutō
• Kikuchi
• Kumamoto
• Nagomi

Ōita Prefecture

• Hita

Yamaga has a humid subtropical climate (Köppen climate classification Cfa) with hot, humid summers and cool winters. There is significant precipitation throughout the year, especially during June and July. The average annual temperature in Yamaga is 14.9 °C (58.8 °F). The average annual rainfall is 2,177.9 mm (85.74 in) with July as the wettest month. The temperatures are highest on average in August, at around 26.3 °C (79.3 °F), and lowest in January, at around 3.5 °C (38.3 °F). The highest temperature ever recorded in Yamaga was 36.9 °C (98.4 °F) on 21 August 2013 and 8 August 2015; the coldest temperature ever recorded was −10.1 °C (13.8 °F) on 19 February 1977.

Per Japanese census data, the population of Yamaga is as shown below,

Historical population

Year	Pop.	±%
1960	76,209	—
1970	64,029	−16.0%
1980	62,839	−1.9%
1990	62,150	−1.1%
2000	59,491	−4.3%
2010	55,391	−6.9%
2020	49,025	−11.5%

The area of Yamaga was part of ancient Higo Province. 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. During the Edo Period it was part of the holdings of Kumamoto Domain. It was the site of a battle during the 1877 Satsuma rebellion. After the Meiji restoration, the town of Yamaga was established with the creation of the modern municipalities system on April 1, 1889. On January 15, 2005, Yamaga absorbed the towns of Kahoku, Kamoto, Kaō and Kikuka (all from Kamoto District) to create the new and expanded city of Yamaga.

Yamaga has a mayor-council form of government with a directly elected mayor and a unicameral city council of 20 members. Yamaga contributes two members to the Kumamoto Prefectural Assembly. In terms of national politics, the city is part of the Kumamoto 3rd district of the lower house of the Diet of Japan.

The local economy is based on agriculture and light manufacturing.

Yamaga has 15 public elementary schools and six public junior high schools operated by the city government, and three public high schools operated by the Kumamoto Prefectural Board of Education. There is also one private high school. The prefecture also operates a special education school for the handicapped.

Yamaga has no passenger railway services. The nearest train stations are Shin-Tamana Station on the Kyushu Shinkansen or either Tamana Station or Ueki Station on the JR Kyushu Kagoshima Main Line.

The Kyushu Expressway passes through the western part of the city, but there are no interchanges within the city

• National Route 3
• National Route 325
• National Route 443

Attractions include the Kumamoto Prefectural Ancient Burial Mound Museum.

• Yamaga Bon-dancing Lantern Festival, every August event
• Yachioza Traditional Theater

• Benkei-ga-ana Kofun
• Chibusan-Obusan Kofun
• Iwabaru Kofun cluster
• Katōda Higashibaru Site
• Kikuchi Castle ruins
• Kumabe Clan Yakata
• Nabeta Cave Tombs

• Mayumi Aoki, swimmer
• Ryōtarō Araki, football player
• Chiyohakuhō Daiki, sumo wrestler
• Shin'ichi Etō, baseball player
• Daiki Inaba, professional wrestler
• Ikuo Kabashima, politician
• Sō Kawahara, football player
• Kiyoura Keigo, politician
• Raizō Matsuno, politician
• Yorihisa Matsuno, politician
• Kōhei Miyazaki, football player
• Kubushiro Ochimi, suffragist and temperance leader

• Official website (in Japanese)