Oncicola venezuelensis Marteau, 1977 was found parasitizing adults of Leopardus pardalis (Linnaeus) found dead in Serra da Capivara National Park, Piauí state, Brazil, a new geographical locality reported for the species. The diversity of Oncicola Travassos, 1916 species is large, but genetic data are scarce. This article presents the results of genetic, morphological and ultrastructural studies carried out for taxonomic purposes. The first ultrastructural view showed a globular, short proboscis with 36 hooks, divided into six longitudinal rows of six hooks each. Hooks differ in size and shape: hooks I, II and III have a ‘chisel-shaped’ tip. The genetic profile included new sequences of ribosomal DNA ITS1, 5.8S and ITS2, and partial 28S rRNA regions. The results of maximum-likelihood tree analyses for each region showed Oligacanthorhynchidae Southwell et Macfie, 1925 close to Gigantorhynchidae Hamann, 1892 (supported >91%). Both use mammals and birds as definitive hosts. Morphological and ultrastructural studies combined with genetic analysis shed more light on the diversity of Oncicola species.