Archiacanthocephalans are reported from mammals of Paraguay. Oncicola martini sp. n. is described from Felis geoffroyi. It is most similar to O. lamasi (Freitas et Costa 1964) comb. n., differing in having larger hooks, all except the smallest of which are barbed. Other species recorded are Oncicola oncicola from Felis geoffroyi (new host record), O. paracampanulata from Felis yagouaroundi, O. luehei from Nasua nasua, Oligacanthorhynchus microcephala from Didelphis albiventris, and O. tortuosa from Euphractus sexcinctus (new host and South American records).