The Buff-bellied Hummingbird, Amazilia yucatanensis, is a medium-sized hummingbird. It is 10-11 cm long, and weighs 4-5 g.

Adults are a metallic olive green above and buffy in the lower breast. The tail and primary wings are rufous in color and slightly forked. The underwing is white. The bill of the male is straight and very slender. It is red in coloration with a darker tip. The throat is a metallic golden green. The female has a dark upper bill, and is less colorful than the male.

The breeding habitat is in forests and thickets from the lower Rio Grande river Valley in southernmost Texas of the United States through the Yucatán Peninsula of eastern Mexico, ending in northern Belize and northwestern Guatemala in Central America. It prefers pine-oak forests, semi-arid scrub and thickets along watercourses. The female builds a nest in a protected location in a shrub or tree. Both males and females of any age aggressively defend feeding locations within his or her territory. Females lay two white eggs.

This hummingbird is partially migratory. The Buff-bellied Hummingbird winters in small numbers along the Gulf Coast of the United States from Texas to the Florida panhandle.

These birds feed on nectar from flowers and flowering trees using a long extendable tongue or they catch insects on the wing.