The long-tailed reed finch (Donacospiza albifrons) is a species of South American bird in the tanager family Thraupidae.

It is found in Argentina, Bolivia, Brazil, Paraguay, and Uruguay.

The long-tailed reed finch was formally described in 1817 by the French ornithologist Louis Pierre Vieillot under the binomial name Sylvia albifrons.

[2][3] Vieillot based his description on the Cola Aguda del Vientre de Canela that had been described by the Spanish naturalist Félix de Azara in 1805 based on a specimen obtained in Paraguay.

[4][5] The long-tailed reed finch is now the only member of the genus Donacospiza that was introduced in 1851 by the German ornithologist Jean Cabanis.