Nagu (Nauvo in Finnish) is a municipality of Finland.

It is located in the province of Western Finland and is part of the Finland Proper region. The municipality has a population of 1,446 (2003) and covers an area of 247.51 km² of which 3.66 km² is water. The population density is 5.9 inhabitants per km².

The municipality is bilingual, with majority being Swedish and minority Finnish speakers.