A new species of Biacantha Wolfgang, 1954 (Nematoda: Molineidae), is described from the common vampire bat, Desmodus rotundus Geoffroy and St. Hilaire, 1810, from northwest Argentina. Biacantha normaliae n. sp. Oviedo, Ramallo, and Claps, is characterized by the disposition and number of ridges of the synlophe, the excretory pore located on a knob, 2 lateral processes on the tail of females, the male caudal bursa morphology, and lack of gubernaculum. This is the first species of nematode described in a vampire bat from Argentina.