Sulfated inulin was synthesized by sulfur trioxide-pyridine method.The reaction temperature,time, reagent proportion,and the solvent volume were optimized with the degree of sulfate group(DS) as index.The better modified condition was determined,in which reaction temperature was 95℃,reaction time was 4h,reagent proportion of inulin to sulfur trioxide - pyridine was 1:4 and volume of pyridine was 25 mL.The DS was 2.81.The results of IR spectrum and UV-spectrum confirmed the structure of the sulfated inulin.