Abstract: LMWHA with relative molecular weight less than 5,5~10,10~30,30~60ku were prepared by changing the degradation conditions of the microwave combined with hydrogen peroxide and ascorbic acid. Reducing power,scavenging ability on ·OH and DPPH free radical of different molecular weight LMWHA were determined. Results showed that the scavenging ability of DPPH free radical and reducing power increased with molecular weight decreased,while the scavenging ability of ·OH decreased,this phenomenon may be associated with the mechanism of LMWHA removing free radicals,the scavenging ability of DPPH and reducing power of LMWHA depended on the number of the double bonds,but the scavenging ability of ·OH depended on the Hydroxyl groups of LMWHA and the ability of chelating transition metal ions.Therefore,low molecular weight hyaluronic acid had good oxidation resistance.