Abstract: We chose needle mushroom as the research material. Polysaccharides in needle mushroom were extracted by microwave and then modified by sulfuric acid and acetic anhydride-pyridine method. The result showed that they were successfully sulfated and acetylated by infrared spectroscopy. At the meantime, antibacterial activity test showed that the sulfated and acetylated derivatives of polysaccharides had a weaker antibacterial effect. The minimum inhibitory concentration for Escherichia coli and Staphylococcus aureus was between 25mg/mL and 50mg/mL. For one strain, the antibacterial effect got stronger with the growing of mass concentration of the derivatives.