Hisonotus charrua sp. n. is described from the Río de la Plata and río Uruguay basins in the República Oriental del Uruguay. Hisonotus charrua sp. n. is distinguished by the following combination of characters: lateral plates 23-25, posterior margin of pectoral spine smooth, 18 to 24 plates bearing laterosensory canals, snout with an anterior odontode free area, and caudal peduncle depth 10.8-12.3% SL.