Brenthia leptocosma is a species of moth of the family Choreutidae.

This species has a wingspan of 8–9 mm, the head is bronzy-fuscous with a white line above the eyes.

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 spots.

This species is similar to Brenthia cyanaula in markings, but the palpi are quite different and characteristic.