Abstract: One strain of Bacillus named XW4 was isolated from lake mud with a broad spectrum of antimicrobial activity by heat treatment and agar diffusion method. Bacillus XW4 was identified by its morphological and cultural characteristics,physiological and biochemical properties and 16S rDNA sequence analysis. And the antibacterial activity of its fermentation products was also determined. The results showed that the strain XW4 was identified as Paenibacillus polymyxa,and its secondary metabolites had strong antimicrobial activities against some kinds of spoilage microorganisms,including Bacillus subtilis,Staphyloccocus aureus Escherichia coli and Lysinibacillus fusiformis. The cell-free supernatants from Bacillus was sensitive to proteinase k,while without sensitive to papain,trypsin and pepsin. The antimicrobial activity to Escherichia coli was stable after heat treatment with 60,80,100 ℃,and it maintained effective within pH3.0~11.0.