Achterwehr is an Amt 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 Nord-Ostsee-Kanal. The Autobahn 210 from Kiel to Rendsburg passes to the north of Achterwehr, and the river Eider crosses it.