Achterwehr is a municipality, located in the district of Rendsburg-Eckernförde in the German Bundesland of Schleswig-Holstein.

Achterwehr is situated 12 km west of Kiel and about 5 km 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.

Achterwehr is the seat of the Amt ("collective municipality") Achterwehr.