Abstract: An anti-microbial peptide named MSP-Ⅶ,was isolated from the skin secretion of the toad,Bombina maxima,distributed in Yunnan Province of China,by a three step protocol including Sephadex G-75 and G-50 connected with G-25 two steps of the gel filtration and one reverse-phase high-performance liquid chromatography.Fast atom bombardment mass-spectroscopy of MSP-Ⅶ gave a protonated molecular ion m/z 2648 which matched the theoretical molecular weight predicted from the composition of amino acids.It consists of twenty-six amino acid residues determined by automatic amino acid analyzer.MSP-Ⅶ is a water-soluble peptide.MSP-Ⅶ has a strong anti-microbial activity to bacteria,fungi and yeast with a little hemolysis activity.These characterizations of MSP-Ⅶ make it possible to be used as a clinical anti-microbial medicine.We tested its effect on micro-vessel osmosis ability with Evens blue dye.It was found that MSP-Ⅶ made the permeability of some tissues such as lung,liver,small intestine,to Evens blue dye increase.In particular,this peptide obviously increased permeability of lung.In addition,MSP-Ⅶ displayed an effect on the contraction of smooth muscle,which strengthened the contraction ability of rabbit aorta smooth muscle.