The Seibu 30000 series (西武30000系) is an electric multiple unit (EMU) train type operated by the private railway operator Seibu Railway on commuter services in the Tokyo area of Japan. First introduced in April 2008, a total of six 10-car sets, eighteen 8-car sets, and six 2-car sets were built by Hitachi Rail between 2008 and 2016 to replace older three-door 101 series and 301 series sets.^[1] It is nicknamed the "Smile Train" (スマイルトレイン, Sumairu Torein).^[2]

Sets are formed as two-, eight-, and ten-car units, consisting of aluminium wide-bodied (2.93 m (9 ft 7 in)) 20 m (65 ft 7 in) long four-door cars with no end gangway doors.^[2] Six-car sets were also scheduled to be built by fiscal 2011, but none were ultimately delivered.^[1][3]

As of 10 November 2021^[update], the fleet consists of 6 ten-car sets, 18 eight-car sets, and six two-car sets, based at Kotesashi, Minami-Iriso, Musashigaoka, and Tamagawa-Josui depots for use on Seibu Shinjuku Line and Seibu Ikebukuro Line workings.^[3][4]

The last set ordered, eight-car set 38118, was delivered in June 2016, bring the total size of the fleet to 216 vehicles (30 sets).^[4]

Sets are formed as shown below.^[3]

Seating consists of longitudinal bench seating throughout. Wheelchair spaces are provided in the two outermost cars at each end of eight-car sets and in the 32100 cars of two-car sets.^[3] Priority seats are provided at the end of each car.^[3] Sets built from fiscal 2013 feature LED lighting and transparent overhead luggage racks in place of the earlier stainless steel pipe racks.^[5]

The first train entered service on the Seibu Shinjuku Line on 26 April 2008.^[6]

The fleet history details are as shown below.^[3]