By irradiating .sup.60Co .gamma. ray to chitin/chitosan, chitin/chitosan having high molecular weight is separated or decomposed into low molecular weight chitin/chitosan. A method of producing an osteoconduction substance comprises the steps of irradiating .sup.60Co .gamma. ray to chitin/chitosan to produce low molecular weight chitin/chitosan; preparing chitosan sol by dissolving low molecular weight chitin/chitosan in an acidic aqueous solution to obtain a chitosan acidic aqueous solution and kneading the chitosan acidic aqueous solution and apatite powder; and neutralizing the chitosan sol by the use of a neutralizing agent.