The Belgrano Sur line is an Argentine 1,000 mm (3 ft 3+3⁄8 in) metre gauge commuter rail service in the Greater Buenos Aires area, currently operated by state-owned enterprise Trenes Argentinos.

The Belgrano Sur runs over tracks and through stations built by the Franco–Belgian-owned Compañía General de Buenos Aires and British Midland companies at the beginning of the 20th century.

The termini is Dr. A. Sáenz station in the Nueva Pompeya district of the autonomous city of Buenos Aires, with two branches, one to Lozano in General Las Heras Partido (departing from González Catán)[1][2] and the other to Marinos del Crucero Gral.

After the nationalisation, several improvements were carried out on the line, including an additional rail track between Aldo Bonzi and Libertad to increase the frequency of the services.

The modernisation included the purchase of brand-new diesel locomotives manufactured by the American company Whitcomb in 1951 (with the addition of 15 new locomotives from the Dutch company Werkspoor in 1955) and the construction of junctions at the Tapiales and Aldo Bonzi stations that allowed the ex-BA Midland line to connect with the Sarmiento Railway near Haedo in Greater Buenos Aires.

Trains ran without passengers from Puente Alsina to Aldo Bonzi, running back to the Tapiales junction where they then went to the Buenos Aires station.

On 2 March 1977, Decree N° 547 by de facto President of Argentina, Jorge Rafael Videla ordered the closure and dismantlement of more than 4,000 km of rail tracks.

Several General Belgrano Railway lines were closed on 1 May 1977, although long-distance services to Carhué continued operating until August of that year when the last train ran to that city.

With the railway privatisation in Argentina in the early 1990s, the Belgrano Sur line was granted in concession to the private company Metropolitano which started operations in 1994.

[4] However, the Government of Argentina revoked the contract of concession in 2007 due to poor service standards and increasing complaints from users.

[6] In spite of the large government subsidies received by TMB (the Metropolitano's subsidiary that operated the line) a serious decline[7] in the standard of rail services led to the original concession being revoked.

[24] The platforms of the stations would be elevated to match the height of the new rolling stock, while the track was being refurbished on the line, with the Buenos Aires - Tapiales segment receiving completely new rails on concrete sleepers.

A second stage of the project included to extend the viaduct to Plaza Constitución, connecting both lines, Belgrano Sur and Roca.

[1][33] Trains resumed operations to Villars, a small town with 3,000 inhabitants in General Las Heras Partido,[34] in December 2022, after the Government extended the service from Marcos Paz to that city.

[34] Companies that have operated the Belgrano Sur Line since it was established after the 1948 nationalisation are: In August 2015, the first diesel multiple units (DMUs) acquired from CNR Tangshan were put into service.

[44] Prior to the complete replacement of the existing rolling stock by the Chinese DMUs, the line consisted of a variety of diesel locomotives pulling carriages in a number of different combinations.