Santo Antônio de Posse is a municipality in the state of São Paulo in Brazil. It forms part of the Metropolitan Region of Campinas, the urban agglomeration centred on the city of Campinas in the interior of the state.
The municipality covers an area of 154.13 km² and sits at an elevation of 695 m. Its population is 23,529. Nearby cities include Jaguariúna, Campinas, Americana, Holambra, Amparo, Serra Negra, Artur Nogueira, Mogi Mirim, Mogi Guaçu, Cosmópolis and Espírito Santo do Pinhal.