Six species of Loricariidae belonging to the subfamilies Hypostominae (Hypostomus emarginatus, Rhinelepsis aspera, Pogonopoma wertheimeri), Ancistrinae (Panaque cf. nigrolineatus, Hemiancistrus sp.) and Loricariinae (Sturisoma cf. nigrirostrum) were studied cytogenetically. The results show that 2n = 54 represents the basal diploid number for this fish family. Different trends in the karyotypic evolution can be seen among the subfamilies: Hypostominae and Loricariinae species present diversified karyotypic macrostructures, while the Ancistrinae appear to show more conserved karyotypes. Among the Hypostominae, the genus Hypostomus had a wide karyotypic variation (2n = 52 to 80), where centric fissions seem to play an important role in this chromosomal divergence. The nucleolar organizing regions were diversified, and occurrence of multiple NORs was frequent. Heteromorphic chromosomes belonging to distinct sex chromosome systems can also occur infrequently among the Loricariidae.