Rassach is a former municipality in the district of Deutschlandsberg, in the Austrian state of Styria. It lies in the western part of Styria, within the Deutschlandsberg district, an area of rolling hills and farmland west of Graz.
Since the 2015 Styria municipal structural reform, Rassach has been part of the municipality of Stainz rather than an independent municipality. The reform merged numerous small Styrian municipalities into larger administrative units, and Rassach was among those absorbed.
Its administrative association with Stainz, a market town in the same district, is the main fact defining Rassach's current status. The settlement is otherwise a small rural locality in the Stainz area.