Morro do Diabo, State park in Teodoro Sampaio, São Paulo, Brazil

Morro do Diabo is a hill in Teodoro Sampaio, São Paulo, 687 km from the state capital, and gives its name to the 33,845-hectare Morro do Diabo State Park. The park holds tropical seasonal semi-deciduous forest, one of the last large areas of Brazil's upland Atlantic Forest, with many peroba-rosa trees.

The area began as a forest reserve in 1941 and became a state park in 1986. This transformation brought protection to thousands of hectares of remaining Atlantic Forest in the region.

The name Morro do Diabo, "Devil's Hill", refers to the hill that gives the park its name; the sources record no legend explaining it. The park is used for environmental education and scientific research, and it is home to an estimated 1,200 black lion tamarins, an endangered primate found in its Atlantic Forest.

The park lies in Teodoro Sampaio, 687 km from São Paulo city, and covers 33,845 hectares of seasonal semi-deciduous forest. Rain falls mostly in summer, 1,100 to 1,300 mm a year; daily averages run from 13 °C in May–August to 32 °C in January–March. Fishing rules published on 2 October 2008 cover the park and its buffer zone in the Paraná basin.

The park holds an estimated 1,200 black lion tamarins, one of the most threatened primates, and protects a large stand of peroba-rosa (Aspidosperma polyneuron) trees used in reforestation. The park is also home to tapir, peccary, howler monkey, puma and jaguar.