Map - Sasebo, Nagasaki (Sasebo Shi)

Sasebo (佐世保市) is a core city located in Nagasaki Prefecture, Japan. It is also the second largest city in Nagasaki Prefecture, after its capital, Nagasaki. On 1 June 2019, the city had an estimated population of 247,739 and a population density of 581 persons per km2 (1,505 persons per square mile). The total area is 426.06 km2.

The city includes a part of Saikai National Park. Located in the southern part of the city is the Dutch-styled theme park Huis Ten Bosch. The island of Ukujima is also administered as part of Sasebo city.

The area of present-day Sasebo was a small fishing village under the control of nearby Hirado Domain until shortly after the start of the Meiji period. Imperial Japanese Navy Admiral Tōgō Heihachirō, when surveying the coasts of northwestern Kyūshū for the site of a navy base, selected his location based on its protected, deep-water harbor, geographic proximity to China and Korea, and the presence of nearby coal fields. Sasebo Naval District, founded in 1886, became the major port for the Japanese navy in its operations in the First Sino-Japanese War and Russo-Japanese War, and remained a major naval base to the end of World War II. Along with the base facilities, the navy also constructed the Sasebo Naval Arsenal, which included major shipyards and repair facilities.

Sasebo City was founded on April 1, 1902. The city which had 206,000 inhabitants in 1945 suffered severe damage by bombing on June 29, 1945, during World War II. 48% of the city was destroyed. Sasebo was one of the original 17 targets selected for the dropping of the atomic bomb.

After the end of the war, part of the base facilities were taken over by the United States Navy, forming U.S. Fleet Activities Sasebo. Some parts of the base are shared with the Japan Self-Defense Forces, in particular the JMSDF, though the primary base of the JGSDF's Western Army Infantry Regiment is also among the facilities there.