A new subspecies of Anthanassa drusilla, ssp rioverde, is described from Minas Gerais, Southeastern Brazil. This new subspecies is isolated from all other known subspecies of A. drusilla by at least 2000 km, and its closest taxon based on wing pattern is Anthanassa drusilla higginsi, from Cerro Neblina, Venezuela. To our knowledge, the species is endemic to the region of Pocos de Caldas Plateau (Minas Gerais), a region of high natural radiation and heavily impacted by mining. Since the entire geographic distribution and conservation status of this subspecies is unknown, it is highly recommended that immediate measures are taken to minimize the environmental impact on the area of occurrence of this butterfly.