Abstract: Red pigment was extracted from Shanlan when water as solvent with microwave- assisted extraction.Optimization of extraction conditions was carried out through single factor and orthogonal experiments. The red pigment was separated and purified by column chromatography for bacteriostatic experiment. The optimum conditions were obtained as microwave power 300 W,ratio of solid to liquid 1 ∶ 40,temperature 60 ℃ and the extracting time 9 min,and the extraction rate was 0.323%.The red pigment had inhibitory effect on Escherichia coli,Bacillus subtilis,Candida albicans and Staphylococcus aureus,and the minimum inhibitory concentration was respectively 500,400,700,500 mg·L^-1.