The Tobu Koizumi Line (東武小泉線, Tōbu Koizumi-sen), operated by the private railway operator Tobu Railway, connects Tatebayashi Station located in Tatebayashi, Gunma to Nishi-Koizumi Station located in Ōizumi, Gunma as well as Higashi-Koizumi Station in Ōizumi town to Ōta Station in Ōta, Gunma Japan.

The first section of the line from Tatebayashi Station to Koizumimachi Station was opened for passenger service on March 12, 1917, operated by the Chūgen Railway, which was purchased by Tobu Railway company in 1937.

[citation needed] The 3 km Sengokugashi Freight Line (仙石河岸貨物線) from Koizumimachi Station to Sengokugashi Station (仙石河岸駅) opened on April 13, 1939, as a freight-only branch line.

[citation needed] In 1941, Higashi-Koizumi Station to Ōta Station section opened on June 1, 1941, to service the Nakajima Aircraft Company Ōta and Koizumi plants.

[citation needed] The Nishi-Koizumi to Sengoku freight branch closed in 1976, and freight services ceased on the line in 1996.