The present invention is related to a method for preparing low molecular weight hyaluronic acid from high molecular weight hyaluronic acid which is produced by Streptococcus sp. ID9102 (KCTC11395BP). More specifically, the invention is related to a method of reducing the molecular weight of hyaluronic acid uniformly by reacting high molecular weight hyaluronic acid with an activated carbon in certain decomposition condition while maintaining original propertied of its own. The method of the invention for lowering a molecular weight of high molecular hyaluronic acid has a convenient process without the inconvenience of reprocessing for the removal of input materials, or requiring pH treatment, various reaction catalysts, and complicated additional treatment conditions (such as heat treatment) as in a conventional method. Furthermore, the method has an effect for removing impurities. Thus, through the method, it is possible to conveniently and economically produce low molecular weight hyaluronic acid with high purity. The inventive method for lowering the molecular weight has an advantage in that according to a change of a reaction condition using activated carbon, the molecular weight of low molecular weight hyaluronic acid can be variously adjusted. The low molecular weight hyaluronic acid produced by the method of the invention can be produced in accordance with the standards of medical supplies while the hyaluronic acid's own characteristic can be maintained. Also, it can be produced in accordance with the standards of cosmetics or foods.
