Leishmania protozoans are the causal agents of neglected diseases that represent an important public health issue worldwide . The growing occurrence of drug-resistant strains of and severe side effects of available treatments represent an important challenge for the leishmaniases treatment . We have previously reported the leishmanicidal activity of phylloseptin-1 (PSN-1), a peptide found in the skin secretion of (=), against promastigotes . However, its impact on the amastigote form of and its impact on infected macrophages are unknown . In this work, we evaluated the effects of PSN-1 on amastigotes of inside macrophages infected in vitro . We assessed the production of hydrogen peroxide and nitric oxide, as well as the levels of inflammatory and immunomodulatory markers (TGF-β, TNF-α and IL-12), in infected and non-infected macrophages treated with PSN-1 . Treatment with PSN-1 decreased the number of infected cells and the number of ingested amastigotes per cell when compared with the untreated cells . At 32 µM (64 µg/mL), PSN-1 reduced hydrogen peroxide levels in both infected and uninfected macrophages, whereas it had little effect on NO production or TGF-β release . The effect of PSN-1 on IL-12 and TNF-α secretion depended on its concentration, but, in general, their levels tended to increase as PSN-1 concentration increased . Further in vitro and in vivo studies are needed to clarify the mechanisms of action of PSN-1 and its interaction with the immune system aiming to develop pharmacological applications.