Sao Sebastiao is a Brazilian city, located on the southeast coast of Brazil, in the state of Sao Paulo. The population in 2006 is 75,886, its density is 188.1/km² and the area is 403 km². The Tropic of Capricorn lies 25 km north. The municipality existed since 1636 and formed a part of the old hereditary capacity of Santo Amaro.
The island of Sao Sebastiao, which is part of the municipality of Ilhabela is located on the west coast of Sao Sebastiao. Between the city and the island, there is the Sao Sebastiao channel with 30 kilometers in length, and variable width (2km being the shortest crossing). At the channel there is an oil terminal owned by Transpetro, a subsidiary of Petrobas.
The city is famous for its beaches, which makes it a popular tourism destination, specially for people from the state of Sao Paulo.