Present paper described the effect of human tumor necrosis factor alpha (hTNFalpha) and beta (hTNFbeta) on apoptosis induced by ionizing radiation in human embryonic lung cell line 2BS diploid cells and human lung cancer cell line A549 and SPC cells. The results showed that both hTNFalpha and hTNFbeta significantly inhibited 7Gy gamma-ray-induced apoptosis in 2BS cells. In contrast, hTNFalpha or hTNFbeta can increase the sensitivity of tumor cell lines (A549 and SPC cells) to radiation. Therefore, the results suggested that TNFalpha and TNFbeta had potential as a therapeutic agent to protect normal cell from the radiation-induced apoptosis and to sensitize the tumour cells for the damage effect of ionizing radiation.