Abstract: Objective:The fermentation conditions for extracellular polysaccharide production in endophytic fungus HBG16 isolated from Salvia miltiorrhiza Bunge were optimized and its antioxidant capacity was analyzed. Method:Single factor experiment and response surface methodology were applied to optimize carbon source, nitrogen source, inoculation amout and pH of endophytic fungus HBG16.The monosaccharide composition of the sample was analyzed by gel permeation chromatography (GPC). The free radical scavenging ability of extracellular polysaccharide was measured by DPPH method. Results:The results of single factor showed that the carbon source, nitrogen source, pH, and inoculation of fermentation were maltose, yeast powder, pH6.0, and inoculation amout 6%, respectively. The optimum fermentation conditions were maltose 32 mg/mL, yeast powder 2.6 mg/mL, pH6.0, inoculation 6%. And the yield of extracellular polysaccharide reached 0.95 mg/mL under this optimized condition. The polysaccharides were mainly composed of galactose, with a content of 52.09 mg/kg. With the increase of extracellular polysaccharide concentration, the free radical scavenging rate of DPPH was increased. The semi inhibitory amount (IC₅₀) of DPPH free radical scavenging was 0.38 mg/mL. Conclusion:Under the optimized culture conditions, the production of extracellular polysaccharide of endophytic fungus HBG16 was increased from 0.11 mg/mL to 0.95 mg/mL, which laid a foundation for the industrial utilization of fungal polysaccharides.