The purpose of the research: system retrofit of suborder Schistosomatidа in reliance on their morfo-biological distinctions. Materials and methods. Samples of adult and 5 species of larvas have been collected and tested: Schistosoma turkestanicum Skryabin, 1913, Bilharziella polonica (Kowalewsky, 1899), Trichobilharzia ocellata (La Valette, 1854), Dendritobilharzia loossi Skryabin, 1924 and Gigantobilharzia acotylea Odhner, 1910. Adult phases of trematode have been identified in accordance to common methods. Identification of cercaria larva produced by water living shell-fish (Lymnaeidae, Planorbidae, Physidae, Melanoididae) has been carried out according to indicators. Current system of trematode suborder Schistosomatidа - vertebrate animals and man parasites are analyzed. Results and discussion. New variant of system of trematode suborder Schistosomatidа order is proposed. Schistosomatida morfo-biological distinctions and biocycles are taken as a basis. Two families are distinguished in this suborder: Schistosomatidae and Bilharziellidae, which represent parasites of warm-blooded vertebrate animals. There are two families of Sanguinicolidae and Spirorchiidae in suborder Sanguinicolida, which consist of fish and reptile parasites respectively. For Schistosomatida order the new underclass Schistosomatidea is founded. Sanguinicolida order is left as the part of Digenea underclass consisting of androgynous fluke.