Brenthia leptocosma is a species of moth of the Choreutidae family. It is found on Mauritius in the Indian Ocean. This species has a wingspan of 8–9 mm, the head is bronzy-fuscous with a white line above the eyes. The thorax is bronzy-fuscous with five fine white longitudinal lines. The abdomen is dark fuscous. Forewings are elongate-triangular, costa gently arched, dark bronzy-fuscous, irregularly irrorated (speckled) with white and white dots on costa beyond. There is a series of eight small rounded-oblong spots round apex and termen, each centered with a violet-metallic dot. The hindwings are rather dark-fuscous, with a small oblique-oval whitish spot in the middle of the disc, a fine violet-blue-metallic line just before termen from apex to below middle, followed by three or four black