Oppenberg is a former municipality in the district of Liezen in the Austrian state of Styria. It is located in the mountainous region of Upper Styria, within the Rottenmann and Wölz Tauern range area.
Since the 2015 Styria municipal structural reform, Oppenberg has been part of the municipality of Rottenmann. Before that reform, it was an independent municipality with its own local administration.
The area is known for its alpine landscape and small, scattered settlements typical of the Liezen district. Its incorporation into Rottenmann was part of a broader consolidation of municipalities across Styria that reduced the number of independent communes in the state.