This work concerns to the study of Ostracoda of the region 1ying between the beaches of Marbella and Monito, to the north of Cartagena (Bolivar) enclosing an area of ca. 64 km2. The samples correspond to sediments obtained at depths ranging between O and 25 m. 463 specimens, belonging to 24 species of 13 families were found. The best represented families were Trackyleberididae and Cytheruridae. Puriana pustulosa Bold, 1966was found to be the most abundant and best distributed species. The distribution of the species observed in the region was shown to be extensive in fine sediments (sandy-muds) and reduced in coarse sands, according to the pattern proposed by Peypouquet (1971) and Carbonel (1973).