Amagasaki (äˈmägäsäˈkē) [key], city (1990 pop. 498,999), Hyogo prefecture, S Honshu, Japan, a port on Osaka Bay. An important industrial center, with iron and steel factories, chemical plants, and textile mills, it lies on the banks of the Yodo River. It has excellent railroads and canals. Amagasaki has a 16th-century castle.