Eidophasia assmanni sp. nov., a new species of Plutellidae from the alpine zone of Russian Altai Mountains, is described from diagnostic morphology and DNA barcodes. Male adult and genitalia are illustrated, whereas the female sex remains unknown. The species inhabits alpine scree with patchy herbaceous plants and is considered as possible endemic species of the Altai Mountains. An updated checklist of the 13 global Eidophasia Stephens, 1842 species is provided. The likely polyphyly of the genus is discussed from molecular data of the barcode region of the mt COI gene.