Sternarchogiton zuanoni, a new species of electric knifefish, is described from the rapids and waterfalls of Cachoeira de Kaituká along the Rio Xingu at Altamira, Pará, Brazil. The new species is diagnosable from congeners by a unique combination of morphometric and meristic features, details of pigmentation, the pattern of dentition on the dentary, the possession of an edentulous premaxilla, and an unelaborated lower lip. The description of S. zuanoni brings the number of species in the genus to five. The presence of S. labiatus in the Río Orinoco basin is documented and a key to the species of the genus is provided.