Nephelomys maculiventer is a species of rodent in the genus Nephelomys of family Cricetidae. The type locality is in Colombia, at "Sierra El Libano, alt. 6000 ft, Santa Marta District". It was originally described on the basis of 47 specimens, including 34 from Sierra El Libano and 13 from "Valparaiso".N. maculiventer has long and soft fur that is rufous in color on the upperparts and becomes lighter towards the sides.