The development of drug resistance by infectious agents represents a major hindrance for controlling parasitic diseases and has stimulated the search for new compounds. We have previously shown that phylloseptin-1 (PS-1), a cationic peptide from the skin secretion of Phyllomedusa azurea, exhibited potent antimicrobial activity. Now we evaluate the effect of PS-1 on Leishmania amazonensis and Plasmodium falciparum. Concentrations as low as 0.5 microg/mL of PS-1 exhibited antileishmanial activity comparable to that of antimoniate of N-metilglucamine, while the antiplasmodial effect of PS-1 was evident at the concentration of 16 microg/mL, and reached an activity comparable to that of artesunate, at the concentration of 64 microg/mL. The high antiparasitic activity of PS-1, together with the unrelatedness of its chemical structure to any present antimicrobial drug, which prevents the development of cross-resistance, together with its non-toxicity to mammalian cells make this peptide a promising candidate for the treatment of malaria and leishmaniasis.