The line is part of the Seibu Shinjuku group of railway lines and connects suburban areas of western Tokyo to Seibu and JR main lines that run to central Tokyo. The line passes through the cities of Higashimurayama, Kodaira, and Kokubunji.
Seibu 101 series, 2000 series, and 3000 series EMUs are used on this line. These trains are painted in Seibu Railway's distinctive yellow livery. All trains are local services and stop at all stations. Trains take 12 minutes to complete the 7.8 km journey. The line is mostly single track between Higashi-Murayama and Koigakubo, but with double track sections at each station. Track between Koigakubo and Kokubunji is double track for the first 1.2 km and single track the last 0.9 km before Kokubunji station. The track changes from double to single at Hanesawa (羽根沢信号場,Hanesawa shingōjō?). The 1.2 km double-track section allows 8 trains per hour to operate in each direction during peak. At Kokubunji Station, trains use only a single platform (platform 5) at the terminus.
The line was opened in 1894 as part of the Kawagoe Railway linking Kokubunji and Hon-Kawagoe. At this time, Ogawa was the only intermediate station on the Higashi-Murayama to Kokubunji section. In 1927, the Kawagoe railway was diverted at Higashi-murayama to a new section of track to Takadanobaba and so the Kokubunji line was formed from the orphaned section. The line was electrified in 1948. Two additional intermediate stations were later opened between Ogawa and Kokubunji: Takanodai opened in 1948, and Koigakubo opened in 1955. Setting up of Hanesawa and to double track from Koigakubo to Hanesawa is in 1968. Since July 2008, recorded announcements on trains have been provided in English in addition to Japanese.