Rineloricaria reisi, R. stellata, and R. zaina are registered for the first time in freshwaters of Argentina. These three species were found in the Río Uruguay basin in Misiones Province. As a result of these findings, five species of Rineloricaria are found in the Río Uruguay basin in Argentina. A key of Rineloricaria species from that basin is also provided.Facultad de Ciencias Naturales y Museo