Falcaustra donanaensis sp. nov. (Nematoda, Kathlaniidae) from the large intestine of Mauremys leprosa (Testudines, Bataguridae) is described. By the absence of pseudosucker, arrangement of the male caudal papillae and the size of the spicules Falcaustra donanaensis sp. nov. resembles only to Falcaustra washingtonensis [Bursey and Aker (2001) J Parasitol 87:1082-1084], a species from Ambistoma tigrinum melanostictum in the Nearctic Region. Papillae pattern in the male of F. washingtonensis is similar to F. donanaensis, but differs by the presence of a median papilla in the American species, length of pharynx, spicule, and gubernacle in males, size of eggs, and number of eggs in female. This is the first species of Falcaustra reported in freshwater turtles in the Iberian Peninsula.