A new species of Trichuris is described. Trichuris pardinasi n. sp. was recovered from Phyllotis xanthopygus Waterhouse (Rodentia: Muridae: Phyllotini) in Sierra de la Ventana, Buenos Aires Province, and Pampa de Achala, Córdoba Province (Argentina). This is the first record of Trichuris parasitizing Phyllotini rodents. The new species can be differentiated from the other 10 species parasitizing rodents from South America by the absence of the spicular tube, spicular sheath with spines uniformly distributed, the length of spicule, the J-shaped proximal cloacal tube, and the nonprotrusive vulva. Also, a description of the bacillary band is provided. The present and the future findings of shared parasite fauna from both populations of P. xanthopygus in these disjunct areas will support the hypothesis of a continuous distribution of this host species at a past time.