The Seibu Tamagawa Line (西武多摩川線, Seibu Tamagawa-sen) is an 8.0 km railway line in the western suburbs of Tokyo operated by the private railway operator Seibu Railway. The line connects Musashi-Sakai Station on the Chūō Main Line with Koremasa Station along the Tama River. The line has only six stations and is not connected to any other part of the Seibu Railway system.