Peculiarities of chromosome sets of 4 schistosome species, parasitic in different mollusks from the Chaun lowland were investigated. The karyotype of parthenitae of Trichobilharzia sp. 1 (the intermediate host Sibirenauta picta) consists of 18 elements, of which the 2nd and 6th pairs are submetacentric-metacentric, the other chromosomes are metacentric. The diploid chromosome set of Trichobilharzia sp. 2 (the intermediate host Anisus acronicus) includes 16 biarmed units. The first pair of metacentric chromosomes amounts to 28.02% of the whole haploid set length. Austrobilharzia variglandis have 14 biarmed autosomes and 2 sex chromosomes. Females are the heterogametic sex, Z-chromosomes are of a metacentric-submetacentric type, W have an acrocentric structure. The chromosome complex of Shistosomatium sp. (the intermediate host Lymnaea zazurensis) consists of 14 elements, of which the largest pair is sex chromosomes. The female sex is determined by an exclusively large metacentric Z-chromosomes (relative length 38.36%) and a small acrocentric W-chromosome (relative length only 7.08%). The chromosome sets of Schistosomatium sp. have undergone the most considerable evolutionary transformations among schistosomes, as a result it has the least linkage groups of genes and the most expressed differentiation of sex chromosomes.