With bean dregs as raw materials,sulfated bean dregs polysaccharides were prepared by chlorosulfonic acid-pyridine method.According to the degree of substitution,the sulfating reagent proportion,esterification reagent and polysaccharide solution ratio,reaction temperature,and reaction time were optimized through single factor and orthogonal experiment;The scavenging effects of sulfated polysaccharide on the hydroxy free radical and DPPH· were researched by Phenanthroline-H2O2 method and colorimetric methods.The results showed that the optimums are as follows: the esterification reagent proportion(chlorosulfonic acid∶ pyridine) 1∶ 3,esterification reagent: polysaccharide solution 4∶ 3(volume ratio),reaction temperature 80 ℃,and the reaction time 2.5 h.Under the above conditions,the degree of substitution of bean dregs polysaccharide reached to 2.15.The scavenging effects of sulfated polysaccharides on the hydroxyl free radicals and DPPH· were improved greatly compared with untreated ones.