The relationship between macrobenthic communities and environmental parameters in the Oum Er Rbia estuary was investigated during the summer season. Salinity, temperature, dissolved oxygen and sediment characteristics varied throughout the estuary. Significant spatial differences in the macrobenthic community structure and composition were found along the estuarine gradient, however salinity and sediment characteristics seemed to be the major factors controlling the differences in the assemblages' composition. Nevertheless, each assemblage was found in a particular physico-chemical environment and had a specific species composition depending on environmental conditions. A total of 30 macrobenthic taxa were identified, most of which were typical of brackish and marine waters. Species richness ranged from 1 to 21 species, with an average of 6.64 ± 6.02 species, whereas abundance ranged from 1 to 2501 indiv., with an average of 288.73 ± 736.81 indiv. Diversity values were generally low (< 3) due to the high dominance of few species. Cerastoderma edule was most numerous comprising 70.34% of the total number specimens gathered, followed by Hediste diversicolor (7.43%). Three species communities were identified: The Melita palmata community lived in the lower section of the river with a stronger marine influence and a sandy bottom. The middle section was occupied by the C. edule community on sandy-muddy substrates and included two sub-communities dominated by M. palmata and H. diversicolor. The upper section with a muddy substrate was the habitat of the H. diversicolor community and was also characterized by the lowest numbers of species and individuals in the entire Oum Er Rbia estuary.