The increasing in last years of strains of microorganisms that can resist several antibiotics has stimulated a search for natural products with bactericidal and fungicidal properties, which may have therapeutics applications. Over 750 antimicrobial peptides from a variety of eukaryotic species are now listed on databases, although relatively few have been described for teleosts. For several animal taxons, antimicrobial peptides are key components of the secretions of mucosal surfaces, where undoubtedly they help to protect the underlying tissues from opportunistic or pathogenic microorganisms. Skin of Neotropical warm-water fish is a high risk area for infection because it is devoid of a keratin layer capable of protecting it against scratching, which expose fish skin to infections since these animals dwell in a microbe-rich environment. In order to learn whether peptides from skin mucus of Neotropical fishes have high antimicrobial potency, surface mucus of pacu, tambacu, tambaqui and tilapia was collected by scraping the lateral surfaces of fish and diluted with distilled water. The diluted secretions were centrifuged at 100.000 x g for 1 h at 4°C and the resulting supernatant was passed through a filter to separate polypeptides molecules lesser than 10 kDa. Filtrate antimicrobial activities were tested against Escherichia coli ATCC 25922 and 35218, Staphylococcus aureus, Pseudomonas aeruginosa, Enterococcus faecalis, Leishmania brasiliensis and L. amazonensis. Skin mucus of three species showed antimicrobial activity: pacu and tilápia (antibacterial) and tambacu (antileishmanial).