A new species of Cosmoclopius Stål, 1866, C. joceliae sp. nov. is described based on specimens collected in northern Argentina. This new species is recognized by the vertical and truncate median process of pygophore, and the short-recurved spine on the apex of the dorsal phallothecal sclerite; and other features such as the dorsally black head, pronotum, and femora, and the thoracic sterna black with median pale markings; some females show lighter posterior pronotal lobe and femora with more conspicuous dark and pale bands. Digital images of the adult male and female and male genitalia are provided, as well as a comparison with the species of the genus are given.
Keywords: Hemiptera, Harpactorinae, Cosmoclopius joceliae, new species, Neotropical.