Peckoltia is one of the 26 genera that constitute the Ancistrini. Although Peckoltia has been reviewed recently, its taxonomic status is not fully resolved and not easily distinguished from Hemiancistrus. Neither Peckoltia nor Hemiancistrus have any recognized synapomorphies supporting their monophyly. In this paper we describe a new species of Ancistrini from Rio Xingu drainage, Pará State, Brazil, and assign it to Peckoltia based on its deep body, presence of large odontodes on the cheeks, and lack of carenate plates on the body. The new species can be easily distinguished from all its congeners by its dorsal-fin color pattern (presence of dark thin stripes in the interradial membranes parallel to fin rays that fragment into small spots in larger specimens vs. bands, spots, dots, or membranes with a darker coloration in all other species). Peckoltia feldbergae, new species, differs from all its congeners except P. bachi, P. oligospila, and P. sabaji by having dark brown spots on the entire body (vs. presence of dark transversal bars on the body or a uniform color). Peckoltia feldbergae, new species, can be distinguished from P. oligospila and P. sabaji by a smaller postanal length (28.4–32.4% of SL vs. 34.3–38.8 and 35.7–41.0%, respectively). The description of this species is part of an effort to improve our knowledge about the remarkable diversity of rapids-dwelling loricariid catfishes that are greatly threatened by the construction of several large hydroelectric dams in Brazilian Amazon, and to provide a scientific name for a species exploited by the international aquarium fish trade.