A new species of Heligmonellidae nematode, Guerrerostrongylus gomesae n. sp., is described from specimens collected from the small intestine of the rodent Oecomys mamorae Thomas, 1906 in the Brazilian Pantanal. It differs from the 2 other species of the genus by the number of ridges in the synlophe 35–46 and 40–48 at the midbody in the male and female, respectively, by rays 8 arising at midlength of the dorsal trunk, ending near the margin of the caudal bursa, and the dorsal ray divided at the second–third part into 2 branches, each branch divided into 2 subequal subbranches. In addition, specimens of Guerrerostrongylus zetta Travassos, 1937 collected in Oligoryzomys nigripes Olfers, 1818 contain synlophe with 36–42 cuticular ridges in males and 38–42 in females at the midbody. By the characteristics of the synlophe and caudal bursa, Gerrerostrongylus gomesae n. sp. is considered a new species. We suggest that the number of cuticular ridges for this genus broadens the range of the cuticular ridges to at least 35 at midbody.