The plain-bellied emerald (Chrysuronia leucogaster) is a species of hummingbird in the "emeralds", tribe Trochilini of subfamily Trochilinae. It is found in Brazil, the Guianas, and Venezuela.
The plain-bellied emerald is 9 to 10 cm long. Males weigh 4 to 4.5 g and females about 4.3 g. Adults have a short, straight to slightly decurved, blackish bill with a red base to the mandible. Adult males of the nominate subspecies C. l. leucogaster have a glittering green crown and sides of the neck. The rest of its upperparts, flanks, and sides of the throat are golden- to bronze-green. The center of its throat and underparts are white. Its inner tail feathers are bronze-green to bronze and the outer ones bluish black. Adult females are similar to the male but have greenish spots on the sides of the throat and grayish green tips to the tail feathers. Immatures resemble the adult female with the addition of brownish edges to the feathers of the back. Subspecies C. l. bahiae is very similar to the nominate but less bronzy.