A study has been made on the geographical distribution and comparative external and cranial morphological analysis of Artibeus lituratus Olfers, 1818 and Artibeus fimbriatus Gray, 1838 (Chiroptera, Phyllostomidae) in the state of Rio Grande do Sul, Brazil. A. lituratus and A. fimbriatus were found to be sympatric in the state north to the "Planície Costeira", in the "Depressão Central", in the hillsides of "Serra Geral", and in the northern region of the state, areas previously covered by forests. The southernmost point for Artibeus Leach, 1821 distribution is 30º South, and A. lituratus and A. fimbriatus are the two species found more to the south. The two species studied do not show sexual dimorphism as to external characteristics. Cranial measurements revealed significant differences between males and females of A. lituratus in mandible length, which was significantly larger in females(p<5%), and between males and females of A. fimbriatus, in the length of the set of lower teeth and in the external width between the cingula of canine teeth, which were significantly larger in males (p<5%). No further morphological cranial differences were found between genders of both species. A. lituratus and A. fimbriatus can be externally distinguished by size, for A. lituratus is larger than A. fimbriatus as concerns all external dimensions analysed except for the tibia length (p<5%). The two species can also be differentiated by pelage colour, hair length, and facial stripes appearance. In the skull, a number of differences were found in rostrum format, in the developmental degree of supraorbital and post-orbital crests and pre-orbital and post-orbital processes, and in several cranial dimensions analysed.