Achterwehr is a municipality, located in the district of Rendsburg-Eckernförde in the German Bundesland of Schleswig-Holstein.
Achterwehr is situated 12km west of Kiel and about 5km south of the Kiel Canal (German:Nord-Ostsee-Kanal). The Autobahn 210 from Kiel to Rendsburg passes to the north of Achterwehr, and the river Eider crosses it.