Pseudoplatystoma (Bleeker, 1862) species are of commercial importance in the region of Rondônia, however studies with the species are scarce, so the objective of the research was to carry out a diagnosis of the composition and structure of the parasite communities of Pseudoplatystoma fasciatum (Linnaeus, 1766) and P. tigrinum (Valenciennes, 1840) of the river basin Jamari, Ariquemes - RO, Brazil. During the period from November / 2016 to February / 2018, 50 specimens of P. tigrinum and 51 specimens of P. fasciatum were collected. Of the total sampled fish, 45 specimens of P. tigrinum and 51 specimens P. fasciatum were parasitized by at least one species of parasite presenting a prevalence level of 90% and 100%, respectively. In the parasitic infrapopulations of P. tigrinum, the groups with the highest prevalence rates were nematodes, with larvae being the largest representative of the g...