The Rosario and Puerto Belgrano Railway was a French-owned railway company which operated a 5 ft 6 in broad gauge, 5 ft 6 in, single track line between the cities of Rosario and Puerto Belgrano in Argentina. Puerto Belgrano, near the city of Bahía Blanca in Buenos Aires Province, is the main naval base in Argentina. The original idea behind the building of the railway was to link points that were closer to either Rosario or Bahía Blanca than they were to Buenos Aires, thereby taking traffic from the British-owned companies BA Great Southern and BA Western railways.

The Buenos Aires Great Southern Railway (BAGS) was one of the Big Four broad gauge, 5 ft 6 in, British-owned companies that built and operated railway networks in Argentina. The company was founded by Edward Lumb in 1862 and the first general manager was Edward Banfield after whom the Buenos Aires suburban station of Banfield was named, when it opened in 1873. After president Juan Perón nationalised the Argentine railway network in 1948 it became part of the state-owned company Ferrocarril General Roca.