The Rio de Janeiro–São Paulo Megalopolis, also known as the Brazilian Megalopolis^[1] is a megalopolis in Southern Brazil consisting of the cities of Rio de Janeiro and São Paulo, as well as their surrounding urban areas.

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In 1999, Brian J. Godfrey wrote: "Even as Rio de Janeiro and Sao Paulo have sprawled to form the two main nuclei of an integrated megalopolis with a current population of between 30 and 60 million in southeastern Brazil, the two cities retain distinguishing characteristics."^[2]

In 2003, Jean Gottman, who studied the Northeast megalopolis in the 1960s, also suggested the formation of this megalopolis. ^[3]

The entire Rio–São Paulo area is also sometimes considered a conurbation,^[4] and plans are in the works to connect the cities with a high-speed rail. Yet the government of Brazil does not consider this area a single unit for statistical purposes, and any population numbers would be synthetic. Another estimate published by Stanley D. Brunn, et al. suggests a population of 50 million.^[4]

As of December 2013, Rio de Janeiro to São Paulo is the third-busiest air traffic route by passenger volume, according to Amadeus.^[5]