A new species, Piarosoma arunachalensis sp. nov., is described and illustrated based on external characters and the genitalia of two male specimens from Tale Wildlife Sanctuary, Lower Subansiri District, Arunachal Pradesh, India. The new species is distinguished from other Piarosoma by a combination of: a) presence of large hyaline patches on the wings, b) the absence of any white or yellow markings on the patagia and the abdominal segments, and c) differences in male genitalia.