A new species of Hyphessobrycon is described from the Rio Papagaio, a tributary of the Rio Juruena, Rio Tapajós basin, Brazil. The new taxon can be distinguished from its congeners by having a well-defined and relatively narrow dark midlateral stripe on body extending from the upper half of the posterior margin of the eye to the middle caudal-fin rays, absence of a humeral blotch, 16–19 branched anal-fin rays, 2–4 maxillary teeth, six branched pelvic-fin rays, and the absence of dark pigmentation crossing the eye. Hyphessobrycon cyanotaenia, a species described from few specimens from the aquarium trade without precise locality, is redescribed herein based on extensive material, and its known distribution is discussed and rectified from the original description.