Imparfinis comprises 20 valid species in the Heptapteridae, being the most diverse taxonomic group of catfishes of the Nemuroglanis subclade. The genus has one of the widest geographical distributions in the neotropical region, found on both sides of the Andes, from Costa Rica to the Paraná and Uruguay river basins in Argentina. A new species of Imparfinis is described from streams of the upper Rio Tapajós and its tributary Teles Pires in northern Brazil. The new species is diagnosed from all congeners by the presence of a vertical dark brown band W-shaped at the base of the caudal-fin rays, a thick dark brown lateral stripe from the snout to the end of the caudal peduncle, dark brown head, long maxillary barbel surpassing the distal margin of the pectoral fin, and presence of 39 or 40 total vertebrae.