The olivaceous thornbill (Chalcostigma olivaceum) is a species of hummingbird in the "coquettes", tribe Lesbiini of subfamily Lesbiinae.

Adult males of the nominate subspecies are mostly dull dark bronzy or olive green, including the tail.

It has a narrow gorget that is glittering green at the throat and shades through yellow, pink, and purple to blue at its bottom.

[6] The nominate subspecies of olivaceous thornbill is found from Apurímac in southeastern Peru to Bolivia's La Paz Department.

C. o. pallens is found on the western slope of the Peruvian Andes between the departments of Ancash and Junín.

The species is most often found in somewhat humid puna grasslands but also inhabits low scrub and the edges of dense woods of Polylepis and Gynoxys.

It captures small insects by sallying from the ground or by gleaning from low vegetation.