The Atlantic rain forest is in a very fragmented condition due to the high deforestation in recent decades, thus even remnants of secondary vegetation may be considered important for maintaining the ecological and microclimatic functions on a regional scale. This represents the first plant composition study conducted in the area, located in Sorocaba (São Paulo, Brazil), a region relatively unknown in terms of vegetation. Our aims were to survey the vegetation, verify the vegetation formation in which the sampled species occur and identify endangered species. Periodic samples of woody plants were conducted between September 2007 and December 2009. We found 166 species, belonging to 47 families and 102 genera; ten of these species are under threat of extinction. Our data substantially increase our knowledge of the diversity of the regional flora and will play a crucial role in developing conservation policy.