The Seibu Yūrakuchō Line (西武有楽町線, Seibu Yūrakuchō-sen) is an underground railway line operated by the private railway operator Seibu Railway in Japan.

The line started out with the section between Shin-Sakuradai and Kotake-Mukaihara, and began through operations with the TRTA (now Tokyo Metro) Yūrakuchō Subway Line.

Later in 1998, the section between Shin-Sakuradai and Nerima became double-tracked, and through services with the Ikebukuro Line began.

[1] Station numbering was introduced on all Seibu Railway lines during fiscal 2012, with Seibu Yurakucho Line stations numbered prefixed with the letters "SI" (part of the Seibu Ikebukuro group of lines).

[2] From 10 September 2012, 10-car 5050-4000 series sets entered revenue service on the Seibu Yurakucho Line and Seibu Ikebukuro Line, with inter-running through to the Tokyo Metro Fukutoshin Line.