Abstract: Objective To investigate the radiobiological effects of two irradiation protocols on human hepatocarcinoma cells BEL-7402 and hepatic cells QSG-7701. Methods BEL-7402 cells were irradiated by total doses of 0 Gy,1 Gy,2 Gy,3 Gy,5 Gy,7 Gy,9 Gy,10Gy at a dose rate of 3Gy/min. Two different delivery patterns were acute irradiation model with the fraction-delivery-time was 0~4 min; and 3-Dimensional conformal radiation therapy (3DCRT) model with the fraction-delivery-time was lasted 13~15 min. The surviving fractions were determined by classical colony forming assay. The radiobiological parameters were calculated, and cell survival curves were plotted according to “the single-hit multi-target model”. The survivability, apoptosis and cell cycles of BEL-7402 and QSG-7701 cells irradiated by 6MV X-ray with a single dose of 5 Gy, were assessed by methyl thiazole tetrazolium (MTT) assay and flow cytometry ( FCM ). Results The values of D0, Dq, SF2 of BEL-7402 cell line in acute irradiation pattern and 3DCRT irradiation pattern were 1.69 and 1.78, 1.45 and 1.54, 0.625 and 0.654 respectively. The number of apoptotic BEL-7402 cells reached a peak (32%) and showed a lowest survival (65%) at the 12h after irradiation, while irradiated apoptotic rate in QSG-7701 cells showed highest (18%) at the 24h. Apoptosis and survival between the two cell lines at 12h induced by radiation were significant different（P<0.01）. Conclusion The radiobiological effectiveness were able to be influenced by prolonged fraction-delivery-time for 3DCRT. Radiosensitivity was markedly various from cancer and normal cellular line.