Kiso Observatory (Japanese: 木曽観測所: Kiso Kansokujo) is an astronomical observatory located at Mt. Ontake in Japan. The observatory was founded in 1974, originally as a branch observatory of the Tokyo Astronomical Observatory, with the express objective of studying extra-galactic astronomical objects. Since 1988, it has been maintained by the Institute of Astronomy, Faculty of Science, University of Tokyo (Japanese: 東京大学天文学教育研究センター). It is home to the 105 cm Schmidt Telescope. It is currently open for use by astronomers from all over the world.
In 2002, a 30 cm, fully automatic telescope was added with the designation K.3T (Kiso 0.3-meter Telescope). It is mainly used in the observation of variable stars. It has been automated to aid in the making of numerous repeat observations over long periods of time.