The apple soluble dietary fiber was sulfated using ultrasonic-assisted amino acid-N,N-dimethylformamide method. The scavenging effects of sulfated SDF on hydroxyl radical,superoxide anion radical and oxygen radical were studied. From FTIR,the sulfated soluble dietary fiber had the typical sulfated functional groups. The results of antioxidant activity revealed that the scavenging capacities of sulfated SDF on the hydroxyl free radicals,superoxide anion and oxygen radical were improved compared with the untreated ones.