The rufous-tailed flatbill (Ramphotrigon ruficauda) is a species of bird in the family Tyrannidae, the tyrant flycatchers. It is found in every mainland South American country except Argentina, Chile, Paraguay, and Uruguay.

The rufous-tailed flatbill is 15 to 16 cm (5.9 to 6.3 in) long and weighs about 17 to 26 g (0.60 to 0.92 oz). The sexes have the same plumage. Adults have an olive-green crown, a faint pale line behind the lores, and a faint pale eye-ring on an otherwise dark olive-green face. Their upperparts are mostly dark olive-green with bright rufous uppertail coverts. Their wings are mostly blackish with wide bright rufous edges on the flight feathers and tips on the coverts; the latter show as two wing bars. Their tail is bright rufous. Their throat is grayish, their breast mixed olive-green and yellow, their belly olive-green with a yellow center, and their undertail coverts rufous. They have a dark brown iris, a flat black bill with a pale cream or pink base to the mandible, and bluish gray or gray legs and feet.