The Serra dos Reis A State Park () is a state park in the state of Rondônia, Brazil.
The Serra dos Reis A State Park is divided between the municipalities of Costa Marques (14.17%) and São Francisco do Guaporé (85.83%) in Rondônia. It has an area of . It adjoins the Serra dos Reis State Park along its southern boundary. The park is to the south of the BR-429 highway, east of the town of Costa Marques and north of the Guaporé River, which defines the border with Bolivia.
The Serra dos Reis A State Park was created by decree 7.637 of 7 November 1996 with an area of about in the municipality of Costa Marques. The park was bounded by the Serra dos Reis State Park, created by decree 7.027 of 8 August 1995. The State Department of Environmental Development (SEDAM) was made responsible for administration.