Frednes Bridge (Frednesbrua) is a bridge located on Highway 354 in Porsgrunn municipality in Vestfold og Telemark county, Norway.
The bridge crosses the Porrsgrunn River (Porsgrunnselva) at the mouth where the Skien River (Skiensvassdraget) passes out into Frierfjord at the site of Norsk Hydro's factory complex. The bridge was completed in 1995. It is constructed of prestressed concrete with a drawbridge span over the main channel. The bridge has a length of 461 meters, with a main span of 60 meters and clearance for vessels at mean water level is 13 meters.
Frednes was the historic name of an old district of Porsgrunn as well as the name of the Frednes farm. Frednes was purchased by shipping magnate Christen Knudsen who had moved there with his family in 1855. The manor house was expanded in 1865 but burned down in 1952 and was not rebuilt.