A new species of Otocinclus (Loricariidae) is described from tributaries to the Rio Madeira, in the State of Amazonas, Brazil. The new taxon can be distinguished from its congeners by lacking middle abdominal plates between the lateral abdominal plates, and by having the dark spot at the base of the caudal fin separated from the midlateral stripe by an unpigmented or slightly pigmented area, and not extended posteriorly onto the middle caudal-fin rays.