As of 2011, the city has an estimated population of 259,800 and a population density of 609 persons per km². The total area is 426.47 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.
Sasebo has a humid subtropical climate (Köppen climate classification Cfa) with hot summers and cool winters. Precipitation is significant throughout the year, but is somewhat lower in winter
Shipbuilding and associated heavy industries continue to dominate the economy of Sasebo. Adjacent to the naval base is the Sasebo Heavy Industries Co., Ltd. shipyard. Sasebo Station is the westernmost station in the JR passenger train system.