Keisei Chiba Line

The entire line opened in one step on 17 July 1921, between Tsudanuma and Chiba, as an electrified double-track railway. It was built to 1,372 mm gauge — the same track gauge then used across the early Keisei system — and several of its stations were added over the following years as the suburbs along the route filled in. Keisei-Makuhari and other stops were renamed in 1931, and through the 1920s and 1930s the line settled into its role as Keisei's outlet toward Chiba.

The wartime and early post-war years left their mark. In February 1945 the line's legal basis shifted from the Tramways Act to the Local Railway Act, and on 7 July 1945 the Keisei Chiba station building was destroyed in the air raid on Chiba. Several stations carried names tied to a nearby imperial-university engineering faculty during this period before reverting to ordinary place names — the stop known today as Midoridai passed through the names Hama-kaigan, Teidai-kōgakubu-mae, Kōgakubu-mae and Kurosuna before settling on Midoridai in 1971.

The line's most consequential engineering change came on 10 October 1959, when it was regauged from 1,372 mm to 1,435 mm standard gauge, in step with the conversion of the Keisei Main Line. This brought the Chiba Line into a single through-running gauge with the rest of the modern Keisei network. Around the city of Chiba the alignment was also rebuilt: the Shin-Chiba–Keisei-Chiba section was relocated in 1958, raised onto a viaduct that was completed for single-track running in 1966 and double-tracked in 1967, and a new terminal station, Kokutetsu-Chiba-Ekimae (today's Keisei-Chiba), opened in December 1967.

Through-running has shaped the line's modern identity. An early experiment with through-service from the Shin-Keisei Line ran only briefly in 1955. On 1 April 1992 reciprocal through-operation began with the Chiba Kyūkō Electric Railway extending south of Chiba-Chūō — the line that is today Keisei's own Chihara Line — and on 10 December 2006 through-running with the Shin-Keisei Line resumed on a lasting basis. (The Shin-Keisei Line was absorbed by Keisei and renamed the Keisei Matsudo Line in April 2025.) Station renamings accompanied these changes, including the 1987 renaming of Keisei-Chiba to Chiba-Chūō and the opening of Keisei-Makuharihongō in 1991.

In recent years the line has weathered natural disruptions and adjusted its operations. A typhoon-triggered landslide suspended the whole line in September 2010, and services were halted again after the Great East Japan Earthquake of March 2011, with through-running to the Shin-Keisei Line interrupted by the rolling blackouts that followed before being partly restored that June. Four-car operation, long a feature of the line, was discontinued in a December 2018 timetable revision and six-car trains became standard, though four-car running was reinstated in 2022. Today the Keisei Chiba Line functions as a busy suburban feeder, linking Chiba with the wider Keisei network toward Tsudanuma, Matsudo and central Tokyo, and with the Chihara Line reaching further south.

• 192117 July: the entire line opens between Tsudanuma and Chiba as an electrified, double-track railway built to 1,372 mm gauge.
• 1923Shin-Chiba Station opens (24 July), with intermediate stops added along the route as the suburbs develop.
• 193118 November: a round of station renamings (including Makuhari to Keisei-Makuhari).
• 1945The line's legal basis shifts from the Tramways Act to the Local Railway Act (20 February); on 7 July the Keisei Chiba station building is destroyed in the air raid on Chiba.
• 1955A short-lived through-service with the Shin-Keisei Line runs from 21 April and is discontinued on 1 September.
• 1958The Shin-Chiba–Keisei-Chiba section is relocated (10 February) as part of rebuilding around the city of Chiba.
• 195910 October: the line is regauged from 1,372 mm to 1,435 mm standard gauge, in step with the Keisei Main Line's conversion.
• 196617 December: the new Shin-Chiba–Keisei-Chiba viaduct is completed for single-track running.
• 1967The Shin-Chiba–Keisei-Chiba viaduct is double-tracked (24 June) and the new Kokutetsu-Chiba-Ekimae terminal (today's Keisei-Chiba) opens (1 December).
• 19711 October: Kurosuna Station is renamed Midoridai, the last in a chain of renamings of that stop.
• 19871 April: a round of station renamings, including Keisei-Chiba to Chiba-Chūō.
• 19917 August: Keisei-Makuharihongō Station opens.
• 19921 April: reciprocal through-operation begins with the Chiba Kyūkō Electric Railway south of Chiba-Chūō (today's Keisei Chihara Line).
• 200610 December: through-running with the Shin-Keisei Line resumes on a lasting basis.
• 2011Services are halted after the Great East Japan Earthquake (11 March); Shin-Keisei through-running is suspended by rolling blackouts (14 March) and partly restored on 27 June.
• 20188 December: four-car train operation is discontinued in a timetable revision, with six-car trains becoming standard (four-car running was reinstated in 2022).