The aim of this work is to characterize the sedimentary hydrodynamics responsable for the morphological evolution of the beaches adjacent to the Assinie Passe. We opted a posteriori for a sedimentological approach based on granulometric analysis, for which fifty-four sand samples were taken from the three levels of the beach foreshores at varying depths, following four profiles of the two squares. These samples, subjected to physical and numerical processing, yielded graphs whose analysis reveals three granulometric stocks transported by rolling, graded suspension and saltation from coastal dunes and rivers. These predominanttly fine sandy facies are « well classified«, with acuity indices in the mesocurtic, platycurtic and rarely leptocurtic intervals. This approach shows that the beaches adjacent to the Passe of Assinie are governed by a relative sedimentary hydrodynamics, dominaded by the combination of marine currents (tide and swell) and the contribution of fluvial currents. Knowledge of the sedimentary hydrodynamics of beaches adjacent to river mouth is fundamental to the monitoring of coastal erosion and the sustainable management of the evoluting coastal environment.