Melchnau is a municipality in the Oberaargau administrative district in the canton of Bern in Switzerland. Melchnau celebrated its 900th anniversary in 2000. The earliest written evidence for the town dates from about 1100. Melchnau lies in a small valley near the border with the canton of Luzern. It is about equidistant from Bern (40 km) to the southwest and Luzern (35 km) to the southeast.