This is the first record of the nematode parasite Kalicephalus subulatus (Strongylida, Diaphanocephalidae) in Wagler’s snakes, Xenodon merremi (Squamata, Colubridae), collected in Corrientes, Argentina. The species was observed using light and scanning electron microscope (SEM) and compared to previous studies from Tropical America. As for the metric characters, the specimens collected in Argentina are smaller than all of those found so far in other hosts. However, despite the differences in the measurements, some characters such as the dorsal lobe type III and the amphidelphic uterus allow its specific identification. Previously, this genus was found in X. merremi from Argentina but the absence of males precluded their specific identification.