Somatochlora arctica was recorded in 2017 in the nature reserve “Magazyn” in the Sobiborskie Forests (51°27’06”N, 23°37’35”E, UTM: FC80). On a small (1.2 ha), transitional peat bog one imago (18.05.) was observed and one larval exuvium (26.09) was collected. The exuvium was obtained from bare patch overgrown with Sphagnum sp. caused by uprooted Betula pubes-cens, the only place that did not dry in the summer. A peat bog in the reserve “Magazyn” is the first site of S. arctica found in Polish part of the Polesie. The closest sites of the occurrence of this species has been reported in: south-eastern Poland – about 100 km from the described location, in north-eastern Poland – about 140 km, in the central part of the Polesie on Ukraine and Belarus – almost 400 km. For the time being it is difficult to say whether this population is completely iso-lated and may be ephemeral or it is a discrete subpopulation within a metapopulation that also inhabits some other peat bogs in this region. Peatlands of the Polish part of the Western Polesie have been intensively investigated since the early 1990s, therefore this species is very rare; oth-erwise it must have been found earlier. However, its ability to colonize small isolated sites, often clearly astatic may cause that it can be easier to overlook than other tyrphobionts. Taking this into consideration the further studies on optimal habitats of S. arctica are needed in the Western Polesie in Poland as well as the adjacent areas in Ukraine and Belarus.