The survey presents the molluscan fauna from six impoundment systems of two sides (NW and SE) of the Small Carpathians. Altogether 25 species (15 gastropod and 10 bivalve) species were identified in reservoirs and their subsystems (inflows and outlets). The number of species per site ranged from 2 to 12, the mean number of species per site was 7. The mean number of individuals per site ranged from 15 to 905 (mean 174) ind/m². Radix auricularia, R. ovata, Gyraulus albus, Gyraulus parvus/laevis, Hippeutis complanatus and Pisidium casertanum were present in more than 50% of reservoirs. The most abundant and frequent species in the entire area and all subsystems were Pisidium casertanum, Pisidium subtruncatum and Gyraulus parvus/laevis. Faunistic similarity indices indicate moderate degree of beta diversity i.e., differentiation among the sites; good separation of sites by cluster analysis indicates a different composition among inflows/outlets and littoral molluscan faunas of reservoirs.