The white-bellied tyrannulet (Serpophaga munda) is a small species of bird in the family Tyrannidae. It is found in Argentina, Bolivia, Brazil, Paraguay, and Uruguay. It is found in open forest, woodland and various open habitats with scattered trees. It is closely related to, and by several authorities considered a subspecies of the white-crested tyrannulet, which has a yellow belly. There is complete intergradation between them in belly color and they do not seem to differ vocally. Another yellow-bellied (occasionally white-bellied) and on average shorter-tailed, vocally distinct species, the Straneck's tyrannulet, was for a period mistakenly referred to by the scientific name Serpophaga griseiceps, but that name is a junior synonym of Serpophaga munda.