A new species of Gymnotus is described from coastal river systems in the Pernambuco State, Brazil. It is phylogenetically referred to the “Gymnotus carapo group clade” for presenting a clear patch posteriorly at anal fin, two independent pores at dorsoposterior corner of preopercle, a single row of well-developed teeth (most arrowhead-shaped) anteriorly on premaxilla, cleithrum with anterior notch, and by the relative anus to anal-fin distance, pectoral-fin length, and maxilla length. The new species is distinguished from all congeners in the “Gymnotus carapo group clade” by a unique set of characters of uncertain polarity, including the number of dark bands along the body, dark bands along body three to four times wider than pale interbands, with nearly straight margins (never broken anteriorly into irregular dark spots), and bands nearly uniform in color, number of scales above lateral line, number of lateral-line perforated scales to first ventral ramus, number of total pored lateral-line scales, head length, snout length, body depth, number of anal-fin rays, number of pectoral-fin rays, number of precaudal vertebrae, number of teeth on anterior row of premaxilla, and number of teeth along outer row of dentary. The new taxon represents the first species of Gymnotus described from localities in northeastern Brazil, north of the mouth of the rio São Francisco.