This study aimed to investigate the abundance, population structure and reproductive characteristics (size at first maturity and spawning time) of the Amazon river prawn, Macrobrachium amazonicum, captured in northeast Pará, Brazil. This fishing resource is economically important in the area. M. amazonicum was abundant in the region during the study period (August/08 to July/09), especially in the Curral Velho community. During the rainy season however, there was an accentuated decrease in abundance of this resource. Morphometric relationships that presented allometric negative growth showed a larger increment in growth in cephalotorax and carapace length compared to other body structures. The angular coefficient (b), observed in biometric regressions indicated a negative allometry growth in both sexes, showing that individuals grow considerably faster relative to their biomass increment. According to the size at first maturity found in this study, a minimum capture size of 12mm for females and 12.5mm for males, is recommended.