Abstract: The cytotoxicity of bleomycin As on human cell lines derived from liver cancer (BEL-7402), nasopharyngeal cancer (CNE-2) and stomach cancer (MGc-803) was evaluated with clonogenic assay. Bleomycin A₆ was found to be highly active against these three cell lines, especially liver cancer cells. The IC₅₀ value of bleomycin A₆ for liver cancer BEL-7402 cells was 6×10^-11 mol/L. As shown by flow cytophotometry, bleomycin A₆ blocked the growth of liver cancer cells at G₂ phase. At a tolerable dosage level, bleomycin A₆ exhibited remarkable growth inhibiton on human liver cancer xenograft in nude mice with an inhibition rate of 75%. These observations suggest that bleomycin A₆ may be useful in human liver cancer chemotherapy.