Secondary Highway 539A, commonly referred to as Highway 539A, is a provincially maintained secondary highway in the Canadian province of Ontario, located within Nipissing District. Commencing at a junction with Highway 539 in the community of River Valley, the highway extends northwesterly for 13.1 kilometres (8.1 mi) to a point near where the Sturgeon River crosses the boundary between Nipissing and Sudbury District. At this point, the roadway turns northward and continues as Highway 805.