The Seibu 101 series (西武101系) and New 101 series (新101系) are electric multiple unit (EMU) train types operated by the private railway operator Seibu Railway in Japan.

The 101 series began service in 1969, in conjunction with the opening of the Seibu Chichibu Line.

[7] Former Seibu New 101 series trains were also transferred to Ryutetsu, becoming Ryutetsu 5000 series trains.

[8] In 2018, one set received a livery resembling the Ohmi Railway 100 series.

[11] This Japanese rail transport related article is a stub.