A new species of Mastigodryas is described based on 10 specimens collected on the Upper regions of the Negro and Branco River basins, in the States of Amazonas and Roraima, Brazil, and in the northernmost portion of Guyana. Apparently this species is associated with the open areas of the Amazonian region known as “lavrados,” “campos,” and “savannas.” The new species is characterized by the presence of eight supralabials; five dorsal stripes situated on the anterior portion of the body that fade or disappear on the posterior half of the body and exhibit a reddish unicolor pattern; and a hemipenis with an enlarged spine situated on the left side of the sulcus spermaticus. The new species is similar to Mastigodryas pleei and, herein, included in the pleei group, along with M. pleei, Mastigodryas amarali, and Mastigodryas bruesi.