Objective: The aim of the study was to investigate the impact of 60Co γ-ray on apoptosis, cell cycles and the expression of protein hypoxia-inducible factor-1α (HIF-1α) to Hep-2 cell line in the conditions of normoxia and hypoxia. Methods: Hep-2 cell were divided into 2 groups: group A (normoxia) and group B (hypoxia). All of the cells were exposed to γ-ray with dosage being 0, 1, 3, 5, 10, 20, and 40 Gy. Flow cytometry was used to measure the protein level of HIF-1α and to detect apoptosis and cell cycles. The protein level of HIF-1α was also determined by immunohistochemistry and Western blotting. Results: The protein level of HIF-1α in group B was significantly higher than that in group A. In group A, low doses (1-5 Gy) of γ-ray had caused G0/G1 cell cycle arrest and high doses (10-40 Gy) had caused G2/M cell cycle arrest. In group B, without exposure of γ-ray (0 Gy) had caused G0/G1 cell cycle arrest, all of the different dosage of γ-ray could cause G2/M cell cycle arrest. The curve of apoptosis rate in group A was a parabola, the apoptotic rate was related to the dosage of γ-ray in a dosage dependent manner. The peak was at the point of 5 Gy. The apoptosis rate in group A was significantly higher than that in group B. Conclusion: Different doses of γ-ray could cause different cell cycles arrest then make different impact on apoptosis to Hep-2 cell. The lower apoptosis rate in condition of hypoxia maybe has a relationship with G2/M cell cycle arrest. Up-regulated HIF-1α protein may be one of the reasons for G2/M cell cycle arrest. Objective: The aim of the study was to investigate the impact of 60Co γ-ray on apoptosis, cell cycles and the expression of protein hypoxia-inducible factor-1α (HIF-1α) to Hep-2 cell line in the conditions of normoxia and Hypoxia. Methods: Hep-2 cells were divided into 2 groups: group A (normoxia) and group B (hypoxia). All of the cells were exposed to γ-ray with dosage being 0, 1, 3, 5, 10, 20 , and 40 Gy. Flow cytometry was used to measure the protein level of HIF-1α and to detect apoptosis and cell cycles. The protein level of HIF-1α was also determined by immunohistochemistry and Western blotting. Results: The protein level of HIF- 1α in group B was significantly higher than that in group A. In group A, low doses (1-5 Gy) of γ-ray had caused G0 / G1 cell cycle arrest and high doses (10-40 Gy) had caused G2 / In group B, without exposure of γ-ray (0 Gy) had caused G0 / G1 cell cycle arrest, all of the different dosage of γ-ray could cause G2 / M cell cycle arrest The curve of apoptosis rate in group A was a parabola, the apoptotic rate was related to the dosage of γ-ray in a dosage dependent manner. The peak was at the point of 5 Gy. The apoptosis rate in group A was significantly higher than that in group B. Conclusion: Different doses of γ-ray could cause different cell cycles arrest then make different impact on apoptosis to Hep-2 cells. The lower apoptosis rate in condition of hypoxia maybe has a relationship with G2 / M cell cycle arrest. Up-regulated HIF-1α protein may be one of the reasons for G2 / M cell cycle arrest.