Abstract: Study the purification and characterization of antimicrobial substance from Bacillus sp.B11.A halotolerant bacterium B11 isolated from saline- alkali soil showed strongly antagonistic against Staphylococcus aureus,and its antimicrobial substance showed excellent stability towards p H,temperature and ultraviolet.The antimicrobial activity was not influenced disposing for 1 h under 100 ℃,and only 11.0% loss of activity was suffered.After treatment at p H3 and p H11,antimicrobial activities decreased 11.4% and 10.9%,respectively,which indicated the antimicrobial substance of Bacillus sp. B11 was stable to acid and alkali. Fermentation broth was used to isolate antimicrobial substances with a procedure involving pretreatment of fermentation broth,cation- exchange chromatography,anion- exchange chromatography,rotary evaporation after butanol extraction,and preparative HPLC on C18 column. Two elution peaks,named A1 and A2,which possessed the antimicrobial activity were eluted with preparative HPLC,and the molecular weight of multi- charge A1 was 1423.8 u.The purified antimicrobial peptide A1 was determined as non- ribosomal synthetic peptide( NRPS) by amino acid analyzer,and its minimum inhibitory concentration against Staphylococcus aureus was 8.0 μg / m L.At the same time,the antimicrobial substance A2 was determined as low- molecular- weight antibiotic substance combined its antimicrobial activity and molecular mass,and its molecular mass was 373 u. Therefore,the antibacterial metabolites from halotolerant bacterium B11 may have potential application in food industry.