The Saint Lucia black finch (Melanospiza richardsoni) is a species of bird in the family Thraupidae. It is endemic to Saint Lucia, where its natural habitats are subtropical or tropical moist lowland forest, subtropical or tropical dry shrubland, and plantations.

The Saint Lucia black finch is a small (13–14 cm; 18–23 g) brown or black finch-like bird with a strong black bill. The male is all black with pink legs, the female is brown above with a contrasting grey crown and beige underparts. Juveniles are similar to the females.

The similar lesser Antillean bullfinch is larger but has a smaller bill and lacks the pink on the legs. The call is a somewhat bananaquit-like but rough "tick-zwee-swisiwis-you", with emphasis on the second and last notes.

This species has a very small population of only an estimated 250–1,000 adults. It is threatened by habitat destruction and predation by invasive species. The International Union for Conservation of Nature (IUCN) categorizes the species as critically endangered.