A new component of antitumor action TG has been isolated from the ethyl acetate extract of Tripterygium wilfordii (besides Triptolide, Tripdiolide and Triptonide). TG was shown in this study to have obvious antitumor effects. The average life span of H22, S180, EAC and breast carcinoma-bearing mice treated with TG ip x 2 days were 100% more than those of the control mice (P less than 0.01) TG was able to inhibit tumor growth of S37-bearing mice at the dose of 150 mg/kg per day, ig x 3, its inhibitory rate was 42% (P less than 0.01). TG could also inhibit squamous epithelial lung carcinoma induced by 3-methylcholanthrene. The inhibitory rate was 65.13% (P less than 0.05). TG had remarkable killing effect on human HL60 and Daudi cells and two direction effects on function M phi of mouse abdominal cavity in vitro.