Nannostomus grandis spec. nov. from Brazil is described. The new species is closely related to N. beckfordi. The differences are (1) the body depth (N. grandis spec. nov. is more elongated as N. beckfordi, body depth 4,66 to 5,35 vs. 4,3 to 5,0 times in SL), (2) head length (N. grandis spec. nov. has an shorter head than N. beckfordi, 4,464,39 to 4,50 vs. 3,83,5 to 4,0 times in SL), (3) the size of body (N. grandis spec. nov. grows larger than N. beckfordi, max. 46.2 vs. max. 35.0 mm SL), and (4) the coloration in life is completely different (e.g. ventral-fins colourless in N. grandis spec. nov. vs. with milky white tips in N. beckfordi). N. grandis spec. nov. is the largest known species of the genus. This fish was captured and bred in captivity as N. anomalus in the beginning of the 20th century by aquarists (Rachow, 1926). The taxon N. anomalus Steindachner, 1976 is not clearly defined because the fi rst description is not informative, the type specimens are lost and the species is not fi gured in the fi rst description. N. anomalus Steindachner, 1876 is correctly synonymized with N. beckfordi Günther, 1872 by Hoedeman (1950) and Weitzman (1966). The determination of Rachow (1926) is wrong. For this reason the new species is named. It was possible to characterize N. aripirangensis Meinken, 1931 after the discovery of specimens from the Ilha do Arapiranga from 1928 in Museum of Natural History Berlin (ZMB). A neotype of this taxon is designated. The synonymy with N. beckfordi Günther, 1872 is confi rmed.