Abstract: Objective:To modify the oxidized degraded polysaccharides of Tremella fuciformis by phosphate esterification and determine the antioxidant activity of the modified polysaccharides. Methods:The polysaccharides of Tremella fuciformis were degraded by hydrogen peroxide-V_C system and its solubility was determined. The degraded Tremella polysaccharides were modified by phosphorus oxychloride and pyridine as phosphorylating reagents. The structural characteristics of polysaccharides were characterized by Fourier transform infrared spectroscopy. The substitution was determined by phosphorus molybdenum blue method. The antioxidant activities of Tremella polysaccharides before and after modification were compared with the scavenging rate of hydroxyl radicals and DPPH free radicals. Results:The Tremella polysaccharides were degraded and dialyzed to obtain a single component with a relative molecular mass of 7.82 kDa. The results of infrared spectroscopy indicated that the modified Tremella polysaccharides had phosphate bond formation at 1262.22、540.55 cm^-1. The degree of substitution was 0.021.Water solubility was 42.71±1.67 mg/mL. The modified Tremella polysaccharide had a significant dose effect on the scavenging effects of hydroxyl radicals and DPPH free radicals. The activity was highest at the concentration of 2.4 mg/mL,and the DPPH clearance rate of the modified Tremella polysaccharides reached 73.77%. The scavenging efficiency of hydroxyl radicals reached 67.45%. Conclusion:Oxidative degradation enhanced the water solubility of Tremella polysaccharides,and the phosphorylation modification enhanced the antioxidant capacity of Tremella polysaccharides.