The moth genus Plutella Schrank, 1802 (Lepidoptera, Plutellidae) includes 26 described species. In addition to the diamondback moth, P. xylostella (Linnaeus, 1758), which is an important and widely distributed pest of cruciferous crops, only two species have been previously recorded in Chile, both with distribution ranges restricted to the southern temperate rainforests. Plutella copaquillaensis sp. nov. is described and illustrated, based on adults reared from larvae collected on Neuontobotrys lanata (Walp.) Al-Shehbaz (Brassicaceae) in the arid highlands of the Andes of northern Chile. The new species resembles P. xylostella in wing pattern, but clearly differs in genitalia morphology.