The large-billed antwren (Herpsilochmus longirostris) is a species of bird in subfamily Thamnophilinae of family Thamnophilidae, the "typical antbirds".

[3] Its relationship to others of its genus is unclear but it apparently is most closely related to the pectoral antwren (H. pectoralis), and at least one author has considered them to form a superspecies.

Adult females have a rufous-cinnamon crown, cinnamon-tinged gray ear coverts and upperparts, and cinnamon neck, throat, and underparts.

Its Brazilian range is roughly bounded by the states of Mato Grosso, Tocantins, and Paraná though it is found locally as far northeast as southern Ceará and Piauí.

It forages actively and methodically, and usually captures prey by gleaning from leaves, stems, and vines by reaching and sometimes lunging from a perch.

It also makes short sallies to access leaves and occasionally takes prey from atop leaf litter on the ground.

[5] The large-billed antwren's breeding season has not been fully defined but appears to span September to December in western Brazil.

The large-billed antwren's song is a "high, fast, chattering series, rising at start, descending and decelerating at end".