The present invention provides an antimicrobial peptide, monodoncin, which is isolated and purified from Penaeus monodon and is capable of being mass produced by molecular cloning techniques in a heterologous expression system, such as yeast. Monodoncin demonstrates a wide-range of bacteriostatic and bactericidal effects on G(-) and G(+) bacteria as well as fungicidal activities, and can be used in combination with conventional antibiotics as "cocktail therapy" to improve the therapeutic effects of the conventional antibiotics.