In most reports, cells involved in the research of comparison of the raidiosensitivity often derived from the same tissue and there are few reports about the comparison of the radiosensitivity among cells from different tissues. Our study selected three malignant human tumor cells from different tissues. The three kinds of tumor cell lines were human hepatoma SMMC-7721 cells, HeLa cells and human melanoma A375 cells. After irradiated with 60Co γ-rays, the survival fractions of the three cell lines were studied by colony-formation assays. D50 (the dose of radiation necessary to reduce the survival fraction to 50%) and α/βwere obtained from dose survival curve . In most reports, cells involved in the research of comparison of the raidiosensitivity often derived from the same tissue and there are few reports about the comparison of the comparison of the radiosensitivity among cells from different tissues. Our study selected three malignant human tumor cells from different tissues. The three kinds of tumor cell lines were human hepatoma SMMC-7721 cells, HeLa cells and human melanoma A375 cells. After irradiated with 60Co γ-rays, the survival fractions of the three cell lines were studied by colony-formation assays. D50 (the dose of radiation necessary to reduce the survival fraction to 50%) and α / βwere obtained from dose survival curve.