Saiki is a city located in the Ōita Prefecture of Japan. It serves as one of the primary municipalities within the region, characterized by its significant geographic scale.
The city covers a total area of 903.11 km2 (348.69 sq mi), which makes it the largest city by area in Kyushu. As of October 31, 2023, Saiki had an estimated population of 65,870 residents distributed across 32,921 households, resulting in a population density of approximately 73 persons per km2.