The Tamagawa Line, or Seibu Tamagawa Line(西武多摩川線,Seibu Tamagawa Sen?), part of the Seibu Railway system, is an 8.0 km railway line in the western suburbs of Tokyo. The line runs from Musashi-Sakai Station on the Chūō Main Line to 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. The line is single-track: trains travelling in opposite directions pass each other as necessary at the stations, which are double-tracked.
The railroad was originally established in 1910 as a freight line, conveying gravel from the Tama River, but freight operations ceased in 1967. In 1927, it was absorbed by the Seibu Railway.