Chūō Line (Osaka Metro)

The line began as the fourth route of Osaka's municipal subway network. Its first section, between Ōsakakō and Bentenchō, a distance of 3.1 km, opened on 11 December 1961; this stretch is generally cited as the first elevated portion of the Osaka subway. The route was extended eastward on 31 October 1964, when the 3.7 km section from Bentenchō to a temporary Hommachi station opened.

For several years the eastern part of the line developed separately as a short shuttle. On 30 September 1967 a 1.3 km segment opened between Tanimachi 4-chōme and Morinomiya, and on 29 July 1968 it was extended a further 2.3 km from Morinomiya to Fukaebashi. The two halves of the line were finally joined in 1969: the permanent Hommachi station was completed on 1 July, and on 6 December the Hommachi–Tanimachi 4-chōme link opened and the through route was given the name "Chūō Line."

The line was completed to its eastern terminus on 5 April 1985, when the 3.2 km section from Fukaebashi to Nagata opened. This set the stage for inter-company through services. On 1 October 1986 the Kintetsu Higashi-Osaka Line — today's Keihanna Line — opened between Nagata and Ikoma, and through-running between the two lines began, extending Chūō Line trains out of central Osaka and into the hills to the east.

Through services were lengthened on 27 March 2006, when the Kintetsu Keihanna Line was extended from Ikoma to Gakken-Nara-Tomigaoka and the through-operating section was carried out to that new terminus. Meanwhile the western end of the line had been reaching out across Osaka Bay: the Osaka Port Transport System's OTS Technoport Line opened the 2.4 km section from Ōsakakō to Cosmosquare at noon on 18 December 1997, and on 1 July 2005 Osaka City acquired this line and absorbed it operationally into the Chūō Line, so that services ran through to Cosmosquare.

On 1 April 2018 the operator changed: the municipal subway system run by the Osaka Municipal Transportation Bureau was corporatised, and the Chūō Line, like the rest of the network, passed to the newly created Osaka Metro Co., Ltd. (Osaka City Transportation Bureau's successor, formally Osaka City Rapid Electric Tramway / 大阪市高速電気軌道).

The most recent change extended the line further into Osaka Bay. On 19 January 2025 the 3.2 km section from Cosmosquare to Yumeshima opened, in preparation for Expo 2025, held on the artificial island of Yumeshima; the Chūō Line thereby became the main rail route serving the exposition site. Today the line is worked by Osaka Metro's own 400 series, introduced from 2023, alongside Kintetsu 7000 and 7020 series sets used on the through services.

• 196111 December: the first section, Ōsakakō–Bentenchō (3.1 km), opens as Line No. 4 — generally cited as the first elevated section of the Osaka subway.
• 196431 October: the line is extended east from Bentenchō to a temporary Hommachi station (3.7 km).
• 196730 September: a separate eastern shuttle segment opens between Tanimachi 4-chōme and Morinomiya (1.3 km).
• 196829 July: the eastern shuttle is extended from Morinomiya to Fukaebashi (2.3 km).
• 19691 July: the permanent Hommachi station is completed. 6 December: the Hommachi–Tanimachi 4-chōme link opens, joining the two halves, and the through route is named the "Chūō Line."
• 19855 April: the line is completed to its eastern terminus with the Fukaebashi–Nagata section (3.2 km).
• 19861 October: the Kintetsu Higashi-Osaka Line (today's Keihanna Line) opens Nagata–Ikoma, and through-running between the two lines begins.
• 199718 December: the OTS Technoport Line (Osaka Port Transport System) opens Ōsakakō–Cosmosquare (2.4 km) at noon.
• 20051 July: Osaka City acquires the OTS Technoport Line and absorbs it operationally into the Chūō Line, so trains run through to Cosmosquare.
• 200627 March: the Kintetsu Keihanna Line is extended Ikoma–Gakken-Nara-Tomigaoka, and the through-operating section is carried out to that new terminus.
• 20181 April: the municipal subway is corporatised; the Chūō Line passes from the Osaka Municipal Transportation Bureau to the new Osaka Metro Co., Ltd. (Osaka City Rapid Electric Tramway).
• 202519 January: the Cosmosquare–Yumeshima section (3.2 km) opens in preparation for Expo 2025, making the Chūō Line the main rail access to the exposition site on Yumeshima.