Cosmopterix xanthura is a moth of the family Cosmopterigidae.

Forewing shining greyish brown, three narrow white lines in the basal area, a subcostal from base to one-quarter, distally slightly bending from costa, a medial from one-seventh to one-third and just above fold, an oblique subdorsal from one-quarter almost to the transverse fascia, a dark yellow transverse fascia beyond the middle with a broad prolongation towards apex and a long and narrow apical protrusion in middle, bordered at the inner edge by two tubercular pale golden metallic subcostal and dorsal spots, the subcostal spot with a patch of blackish scales on the outside and the dorsal spot further from base as the subcostal, beyond the middle of transverse fascia two tubercular pale golden costal and dorsal spots, the dorsal spot twice as large than the costal and more towards base, a greyish brown edged, white costal streak from the outer costal spot, a shining white apical line from the apical protrusion to apex, cilia greyish brown at apex, ochreous-brown towards dorsum.

Hindwing shining brownish grey, cilia ochreous-brown.

Forewing shining greyish brown, the transverse fascia and the apical line indistinctly visible, hindwing shining brownish grey.

Abdomen dorsally yellowish brown, segments whitish edged laterally, segment seven whitish edged posteriorly, ventrally shining dark grey, segments banded shining white posteriorly and with a broad shining yellowish white longitudinal streak, anal tuft yellowish white, dorsally yellowish brown in female.