A study was made on radiolysis of glycyrrhizic acid in dilute aqueous alkaline solution. Radiolysis of glycyrrhizic acid would be divided into two processes: (1) Chromophore (unsaturated ketones) was destroyed; (2) Structure of glycyrrhizic acid was destroyed due to hydrogen abstraction reaction, but chromophore was not destroyed. The G values of radiolysis of glycyrrhizic acid under different atmospheres have been determined. Four radiolytic products were separated by HPLC. Using scavenger method, it showed that glycyrrhetinic acid and unknown products are formed by OH attack. OH attack leads to glucosidic bond rupture. Unknown product is formed by OH and HO,2,. Unknown Ⅲ may be secondary product. Using competition kinetics k,OH-GAH,~10,10,dm,3,mol,-1,s,-1, was got.