The reproductive features of the pea clam Pisidium casertanum in relict lakes of Bolshezemelskaya Tundra were studied. The P. casertanum population in the Vashutkiny Lakes of Bolshezemelskaya Tundra has a single period of summer reproduction. We suppose that the release of embryos mainly occurs between July and August and the breeding season could probably begin in May-June. The positive relationship between brood size and parent shell length was detected. We did not find a specific brooding mechanism, accompanied by asynchronous development and release of embryos by the parent in the population of P. casertanum in the Vashutkiny Lakes. The reason for this is probably related with the environmentally more stable freshwater habitats of the relict Vashutkiny Lakes in comparison with the lakes of the High Arctic.