Kuusjoki () is a former municipality of Finland. It was consolidated with Salo on January 1, 2009.
It is located in the province of Western Finland and is part of the Southwest Finland region. The municipality had a population of 1,781 (2004-12-31) and covered an area of 122.57 kmò of which 0.11 kmò is water. The population density was 14.54 inhabitants per kmò.
The municipality was unilingually Finnish.