Species composition, abundance and distribution patterns of the family Portunidae in the Curuçá estuary in the northeastern portion of the state of Pará (northern Brazil) were studied bimonthly from July 2003 to July 2004. Samples were taken with a wing trawl net during the day at ebb tide during last quarter moon. A total of 427 individuals were collected, comprising three species: Callinectes bocourti, Callinectes danae and Callinectes ornatus. C. danae was the dominant species (56%). C. bocourti demonstrated a preference for the rainy season and C. ornatus preferred the dry season. C. danae was present in both seasons. The results indicate that variation in salinity and pH related to season (dry and rainy) are considered determinant factors for the distribution of C. bocourti and C. ornatus.