Largest in Central Europe ancient and almost intact Belarusian peat bogs are habitats with very specific environmental conditions and biodiversity. They themselves are island-like ecosystems, but in addition they are containing small raised islands of mineral soil within peat, covered by forest. In this study, the ground beetle diversity, species composition and abundance according to their habitat affinity, mean body size and wing form between isolated birch forests on the mineral and peat soils within the peat bog and adjacent continuous birch forests were compared. The diversity respond to isolation most clearly in birch forests with sphagnum cover, while in forests on the mineral soils the diversity parameters were similar to continuous adjacent forests. Distinct separation of carabid assemblages of continuous and isolated habitats was detected only in terms of species composition. There is a clear increase of the abundances of forest species from continuous to isolated forests on mineral soil, whereas in the forests on peat soil specialized peat bog species were dominated. In isolated forests, a gradually decrease of the abundances of large-sized and brachypterous species and increase of medium-sized beetles were recorded. However, the abundance of macropterous species was the most abundant only in isolated forest on mineral soil. Thus, the ground beetle assemblages of the two birch forest types within peat bog respond in a different way to the isolation and recorded differences can be probably explained also a variety of environmental factors.