Formoso River (Rondônia)

The Formoso River (Portuguese: Rio Formoso) is a river of Rondônia state in western Brazil. It is a tributary of the Jaci Paraná River.

In its upper reaches the Formoso River defines the western boundary of the Guajará-Mirim State Park. The park has two support bases on the banks of the Formoso River that are used by researchers and inspection teams.