Abstract: Abstract: Pleurotus eryngii is a kind of valuable edible and medicinal fungus, which contains a lot of effective ingredients. Modern pharmacological researches show that, Pleurotus eryngii fruit body has the function of decreasing blood pressure and reducing blood lipid. Polysaccharides are the main active components of Pleurotus eryngii, which have the antioxidant, antibacterial, antiviral and antitumor effects. The polysaccharide extraction methods include hot-water extraction, ultrasound, microwave, high temperature and high-pressure extraction. At present, the extraction of Pleurotus eryngii polysaccharides is mainly performed by hot-water extraction, which has long extraction time, high energy consumption and low extraction yield. Pleurotus eryngii stalk residue is the byproducts of fruit body processing. It contains rich protein and polysaccharide, and has multiple biological activities and physiological functions, similar with the fruit body. At present, Pleurotus eryngii stalk residue is often used as feed and fertilizer, or directly discarded. The utilization rate of Pleurotus eryngii stalk residue is very low, and it even causes the environment pollution. In 2012, the yield of Pleurotus eryngii in China is about 730 000 tons, and the stalk residue after fruit body processing is about 36 000 tons. Enzymatic treatment is a new technology in food and pharmaceutical industry, which is widely used in extracting biological active substances from animal and plant raw materials, with advantage of high extraction rate, low energy requirement, low cost and simple operation. Microwave assisted extraction is a physical enhancement process of heat and mass transfer, based on traditional extraction process. This method has improved extracting speed, efficiency and quality, compared with conventional extraction process. It has been widely applied to extraction of plant active components. At present, application of enzymatic treatment combined with microwave assisted extraction to extracting polysaccharides from Pleurotus eryngii has not been reported. In this study, the microwave extraction based on enzymatic treatment was used to extract polysaccharides from Pleurotus eryngii stalk residue. The main factors affecting polysaccharide yield (water-material ratio, extraction time and microwave power) were investigated and optimized by response surface design using Design-Expert 7.1.6 software. The enzyme-microwave extraction method was compared with water heating extraction. The antioxidant activities (scavenging capacities on DPPH, hydroxyl free radical and superoxide anion free radical) and antimicrobial activities of Pleurotus eryngii polysaccharides were evaluated. Results showed that, the optimized microwave extraction conditions were as followed: water-material ratio, 35:1 mL/g; extraction time, 15 min, microwave power, 570 W. Under these conditions, the polysaccharide yield was 12.11%±1.02%, which was 41.21% higher than that by water heating extraction method, and the extraction time was shortened by 105 min. The Pleurotus eryngii polysaccharides had certain scavenging effect on DPPH, hydroxyl free radical and superoxide anion free radical, with half maximal inhibitory concentration (IC50) of 22.9, 19 and 21.1 mg/mL, respectively. In addition, the Pleurotus eryngii polysaccharides had good inhibitory effect on Bacillus subtilis, Escherichia coli and Staphylococcus aureus, with minimum inhibitory concentration of 8, 16 and 16 mg/mL, respectively. They had no obvious inhibitory effect on Aspergillus niger or Saccharomyces cerevisiae. This study has provided a technical basis for further development of Pleurotus eryngii polysaccharide functions and utilization of Pleurotus eryngii stalk residue.