This paper reports the first record of the genus Ceratium Schrank, 1973 in six freshwater ecosystems in the semiarid region of Brazil. From 2006 to 2010, 1176 samples were collected from 98 different sites using conical-cylindrical plankton nets with a 25 μm mesh size. Twenty individuals from each sample were measured for the obtainment of the morphological measurements. A 25% NaClO solution was used for the clarification of the cells and visualization of the plates. The appearance of this genus in such ecosystems is likely related to climatic and hydrological changes in the region.