Paecilomyces tenuipes is one of the famous Chinese medicinal entomopathogenic fungi that parasites in the lavae of silkworm. Two cytotoxic components were isolated from methanolic extract of the carpophores of this fungus that was cultivated artificially. Spectral analyses of the cytotoxic components showed that they were known ergosterol peroxide (5alpha,8alpha-epidioxy-24(R)-methylcholesta-6,22-dien-3beta-ol) and acetoxyscirpenediol (4beta-acetoxyscirpene-3alpha,15-diol) that were isolated for the first time from this fungus. The 50% inhibitory concentrations (IC50) of ergosterol peroxide against human gastric tumor cell line (SNU-1), human hepatoma cell line (SNU-354), human colorectal tumor cell line (SNU-C4) and murine sarcoma-180 were 18.7, 158.2, 84.6 and 74.1 microM, respectively. The IC50 values of acetoxyscirpenediol against SNU-1, SNU-C4, SNU-354 and sarcoma-180 were 1.2,4.0, 2.2 and 1.9 microM, respectively. Cytotoxic activities of acetoxyscirpenediol were about 4.0-6.6 times stronger than those of cisplatin which is currently used clinically for cancer patients.