Results based on taxonomic and biostratigraphic studies of marine Cretaceous ostracods collected from the Potiguar and Sergipe basins on the northeastern continental margin of Brazil are presented. The assemblages comprise more than 100 taxa, ranging in age from late Aptian to Campanian. Many taxa show restricted vertical ranges which make them stratigraphically useful. In the Potiguar Basin the Albian–Campanian succession comprises six biozones based on ostracods, whereas in the Sergipe Basin the upper Aptian–Coniacian succession comprises four biozones.