Pennsylvania Route 857 is an 11.04-mile (17.77 km) long state highway located within Fayette County, Pennsylvania, United States. The southern terminus of the route is at the West Virginia state line southeast of Gans in Springhill Township, where the route continues south as County Route 857, a secondary state highway. The northern terminus is at an interchange with U.S. Route 119 and Pennsylvania Route 43 in Uniontown.

The roadway runs parallel to PA 43 for all but one mile (1.6 km) of its length.

One mile north of the state line in Springhill Township, PA 857 connects to the current southern terminus of the Mon/Fayette Expressway (PA 43) via Gans Road. The route continues north to the Springhill Township community of Haydentown, where it intersects PA 43 at exit 4 via Rubles Mill Road. PA 857 continues northward to Fairchance, where it interchanges with PA 43 at exit 8 via Big Six Road. PA 857 then continues past Fairchance before terminating at US 119 (Morgantown Road) just east of another interchange with PA 43 in Uniontown.

The entire route is in Fayette County.