A method for inhibiting free radical is provided. The method includes administering to a subject an effective amount of an herbal composition including Polygonum cuspidatum and/or Viola yedoensis. The herbal composition is suitable for mammalian subjects. The Polygonum cuspidatum is selected from fresh Polygonum cuspidatum herbage, and the Viola yedoensis is selected from fresh Viola yedoensis herbage.
