Petäjävesi is a municipality of Finland.

It is located in the province of Western Finland, next to Jyväskylä and is part of the Central Finland region. The municipality has a population of 3,993 (31 March 2016) and covers an area of 495.39 square kilometres (191.27 sq mi) of which 39.01 km (15.06 sq mi) is water. There are all together 99 lakes in Petäjävesi. The biggest lakes are Jämsänvesi-Petäjävesi, Ala-Kintaus and Ylä-Kintaus. Karikkoselkä is a lake in Petäjävesi, which is formed by a meteorite. The population density is 8.75 inhabitants per square kilometre (22.7/sq mi).