Specific composition, abundance, diversity and dynamics of the Cumacea community from the southeastern Brazilian continental shelf were studied. The area is characterized by the intrusion of a cold and highly saline water mass in summer, the South Atlantic Central Water (SACW), from the slope towards the coast, changing the hydrographic structure of the shelf and the species distribution. During the other seasons the inner shelf, area shallower than 50 m, is filled with warm and low saline water, the Coastal Water (CW). The presence of the SACW seems to favor the abundance and diversity of Cumacea due to its higher primary production and stability. Three groups of species were related to the water masses. Depth and fine sand fraction were shown to be the main factors structuring the Cumacea community. The role of the SACW in maintaining the Cumacea populations in the area through the passive transport of pre-ovigerous and ovigerous females is discussed.