Aistersheim is a municipality in the district of Grieskirchen, in the Austrian state of Upper Austria. It lies in the country's northern Alpine foreland region, within the Hausruckviertel, the traditional quarter of Upper Austria west of the Traun river.
The municipality is made up of a small main village and a number of surrounding hamlets and scattered farmsteads, a settlement pattern typical of the rural Innviertel-Hausruck area. Its landscape is gently rolling, dominated by farmland and patches of woodland.
Aistersheim's most notable landmark is Aistersheim Castle (Schloss Aistersheim), a moated water castle whose origins reach back to the medieval period. The castle and its pond are the defining features of the village and the main point of interest for visitors to the area. The municipality is served by roads connecting it to the nearby towns of Grieskirchen and Haag am Hausruck.