The Mountain Elaenia, Elaenia frantzii, is a small passerine bird in the tyrant flycatcher family. It breeds in highlands from Guatemala to Colombia and western Venezuela. The scientific name celebrates the German physician and naturalist, Alexander von Frantzius.

This tyrant flycatcher is 14-15 cm long and weighs 17-20 g. The upperparts are dull olive, with a narrow white eye ring. The wings are dusky with narrow yellow feather edges and two off-white wing bars. The throat and breast are yellowish grey, becoming dull yellow on the belly. Sexes are similar, but young birds are browner above, paler below, and have brighter wing bars.

This is an inconspicuous species, with a slurred peeeeur call, longer than that of Mistletoe Tyrannulet, and a repetitive d'weet d'weet song.

The Mountain Elaenia breeds between 1200m and 2900m altitude in wet mountain forests, especially at the edges and in clearings, and in adjacent second growth, semi-open areas, or pastures with trees.It moves lower in winter, down to 600 m, and also appears to undergo seasonal movements.

It is solitary when not breeding. It perches on a shaded watchpoint from which it sallies forth to pick insects, spiders, and many berries and seeds from foliage or even the ground. All its food is taken in flight.

Its nest is a cup of mosses, liverworts and lichens, lined with plant fibres. It is built by the female 2-15 m high in a tree or bamboo. The two cinnamon-blotched whitish eggs are incubated by the female for 15-16 days to hatching.