Kasai (加西市, Kasai-shi) is a city located in Hyōgo Prefecture, Japan.
As of 2008, the city has an estimated population of 49,496 and the density of 336.31 persons per km². The total area is 150.19 km².
The city was founded on April 1, 1967 when the towns of Hōjō, Izumi and Kasai were combined to form the city of Kasai.
Kasai is famous for the Gohyaku-Rakan statues (the 500 disciples of Buddha) in Hōjō. Hōjō is also home to Maruyama Park, where one can find the world's largest globe clock (Guinness certified) and reputedly the world's longest roller slide. Other sights in Kasai are the Hyōgo Prefectural Flower Center, the Princess Nehime burial mound, and Ichijō-ji Temple near Zenbo junior high school. Kasai has two festivals: the Saisai festival in early August and the Sekku festival in early April.
Kasai is the sister city of Pullman, Washington USA.