Trössing is a former municipality in the district of Südoststeiermark, in the Austrian state of Styria. It lies in the southeastern part of the country, within the broader Gnas area of the Styrian hills.
Since the 2015 Styria municipal structural reform, Trössing is no longer an independent municipality and has been part of the municipality of Gnas. The reform merged a number of small Styrian communes into larger administrative units.