In this paper the author proposes a new species of the genus Contracaecum Railliet et Henry, 1912. Of the species under Contracaecum, Contracaecum clavatum (Rudolphi, 1809) Baylis, 1920 is the nearest to Contracaecum fortalezae sp. n. differing from the latter by the following aspects: The males have unequal spicules. The females have a short ovijector and parallel uteri directed backward and the eggs are smaller. In both sexes the intestinal cecum is always short and the ventricular posterior appendix is always long, while Contracaecum clavatum presents these structures in an inverse way, considering the lenght of them. Besides, the thorn-like formations at the posterior end of the body are different.