Provided is a process for preparation of a Rhus verniciflua extract, comprising extracting allergen-removed Rhus verniciflua with a soluble solvent, thereby obtaining an extract, subjecting the thus-obtained extract to ultrafiltration to remove high-molecular weigh substances, concentrating and drying the resulting material, thereby obtaining extract powder and irradiating far-infrared to the extract powder, thereby improving anti-cancer activity. The Rhus verniciflua extract prepared according to the process of the present invention exhibits superior anti-cancer activity.