The palaemonid shrimp Macrobrachium amazonicum is widely distributed in coastal rivers, estuaries and inland waters of South America. Despite this, little is known regarding its biology in the natural environment. Furthermore, this species is economically important because it is the main freshwater shrimp commercially exploited by artisanal fisheries in northern and northeastern Brazil, besides showing great potential for aquaculture. Considering this, the present study aimed to analyze aspects of the reproductive biology of M. amazonicum. A total of 251 females were analyzed, 102 of these being ovigerous. The carapace length ranged from 6.03 to 10.06 mm (average ± standard deviation: 7.52 ± 0.84 mm). Reproduction was continuous with a gradual increase from April to June 2012. No significant relationship between frequency of ovigerous females and environmental variables was observed. The fecundity showed a positive linear relation with the carapace length and the number of eggs varied from 33 to 389 (average ± standard deviation: 203 ± 78.06 eggs/female). A dominance of eggs at an early stage was observed in most months. There was an increase in the size/volume of eggs from early to late embryonic stage. Ovigerous females produced eggs at the same development stage, with the same size and volume regardless of their body size. The results demonstrated higher similarity of this population to other continental M. amazonicum populations than from estuarine ones, showing the environment influence in the life-history of individuals.