The emerald-bellied puffleg (Eriocnemis aline) is a species of hummingbird in the "brilliants", tribe Heliantheini in the subfamily Lesbiinae.

[3] It is closely related to the colorful puffleg (E. mirabilis) and they have variously been deemed sister species or superspecies.

Subspecies E. a. dybowskii is larger than the nominate but the male's forehead patch is smaller and the white breast is less sharply defined.

The species inhabits tropical and subtropical montane forest, especially humid types like cloudforest.

[6] The emerald-bellied puffleg forages for nectar in dense vegetation; it usually feeds between about 1 and 3 m (3 and 10 ft) of the ground.

The emerald-bellied puffleg makes "a single, slightly buzzy, metallic note, 'tzit'" call at irregular intervals while hovering.