The black-thighed puffleg (Eriocnemis derbyi) is a species of hummingbird in the Trochilidae family. It is found at humid forest edge and ravines in the Andean highlands of Colombia and northern Ecuador. It is threatened by habitat loss. As suggested by its name, the feathering around its legs is black, which is unique among the pufflegs. Otherwise its plumage is green with a contrastingly black tail.