Aso is a city located in Kumamoto Prefecture, Japan.
The modern city of Aso was established on February 11, 2005, from the merger of the former town of Aso, absorbing the town of Ichinomiya, and the village of Namino.
As of March 31, 2017, the city has an estimated population of 27,039, with 11,355 households and a population density of 72 persons per km². The total area is 376.25 km².
The city is situated within Aso Caldera. The source of the Kikuchi River is located in the city.