Sastamala (Finnish pronunciation: [ˈsɑstɑˌmɑlɑ]) is a town in Finland, located in the Pirkanmaa region. Sastamala lies on both sides of River Kokemäenjoki in the southwest corner of Pirkanmaa. The population of Sastamala is approximately 23,000, while the sub-region has a population of approximately 26,000. It is the 44th most populous municipality in Finland.
Sastamala has an area of 1,531.75 square kilometres (591.41 sq mi) of which 96.14 km (37.12 sq mi) is water, making it the largest municipality in the Pirkanmaa region in terms of area. The population density is 16.4 inhabitants per square kilometre (42/sq mi). The municipality is unilingual in Finnish.