An endophytic bacterium isolated from Sophora alopecuroides in Xinjiang, which had a conspicuous antagonistic effect on methicillin-resistant Staphylococcus aureus (MRSA), was studied and bioactive substances were separated and purified. Strain KDNB6 was identified as Serratia marcescens by its morphological, physiological and biochemical properties and 16S rDNA sequences. An anti-MRSA active component produced in fermentation broth was separated and purified by silica gel column chromatography and sephadex gel column chromatography.