AbstractThe water ratNectomys squamipesis endemic in Brazil and found naturally infected withSchistosoma mansoni. Helminth communities, their prevalences, intensity of infection and abundance inN. squamipesin an endemic area of schistosomiasis in the state of Rio de Janeiro, Brazil were studied. Four species of nematodes (Physaloptera bispiculata, Syphacia venteli,Hassalstrongylus epsilonandLitomosoides chagasfilhoi) were recovered in 85.3%, two trematodes (Schistosoma mansoniandEchinostoma paraensei) in 38.8% and one cestode species (Raillietinasp.) in 1.7% of rats examined. Rats were infected with up to five helminth species each, and these were highly aggregated in distribution. ForH. epsilonandS. venteli, intensities and abundances were higher in adult male and subadult female hosts, respectively.Hassaltrongylus epsilon,P. bispiculata,S. venteliandS. mansoniwere classified as dominant species,L. chagasfilhoiandE. paraenseias co-dominant andRaillietinasp. as subordinated. No significant correlation was found in the intensity of infecton between each pair of helminth species.Schistosoma mansoniwas not related to any other helminth species according to their infection rates, althougthS. mansoniwas well established in the natural helminth comunity of the water rat.