Croton longicarpus (Euphorbiaceae), a new species from southern Brazil, is here described and illustrated. The new species occurs in open vegetation and at the edges of Araucaria forest. The analysis of herbarium collections and observations from populations in the field indicate that the species has characters in common with members of Croton section Lamprocroton. The new species differs from other species in this section by its unusually elongated ovary and fruit, the narrowly spatulate sepals of the pistillate flowers, and long inflorescences.