Campylopus introflexus (Hedw.) Brid. is the most widespread invasive moss species in Europe. Originating from the Southern Hemisphere, it is nowadays causing serious changes in coastal sand habitats of Western Europe and invading various anthropogenic habitats in Central Europe. In South-Eastern Europe, the species was initially found in Croatia in 2013, in the Dinaric region in the karst plain Vrhovinsko polje, on leached bare soil and pine bark remnants. In 2015, another stand of similar size was found in the peri-Pannonian region, on Mt Papuk, on a gneiss cliff in an acidophilous sessile oak forest. These two localities are on the South-Eastern frontline of the species’ invasion within Europe. The oldest individuals were three to four years old, and sporophytes were not found. At the moment, it seems that the invasive moss is not a threat to native flora in the Dinaric region. Nevertheless, special attention should be given to the peri-Pannonian and Eastern Balkan regions, since its expansion could threaten the habitats of native moss and lichen species growing in similar acidic forests. Since the bryoflora of South-Eastern Europe is still largely undersampled, directed surveys and monitoring programs should be promptly established.