Karjalohja (; ) is a former municipality of Finland.
It is located in the province of Southern Finland and is part of the Uusimaa region. Before merging into Lohja, the municipality had a population of (31 December 2012) and covered an area of of which was water. The population density was .
With Nummi-Pusula, Karjalohja was consolidated with the town of Lohja on 1 January 2013.
The municipality was unilingually Finnish.
Prior to its consolidation into Lohja in 2013, Karjalohja contained the following villages:
Results of the 2011 Finnish parliamentary election in Karjalohja: