The work is to investigate effects of ,AdCMV-p53, gene transfer induced by ,60,Co γ-rays on cell cycles of human colorectal adenocarcinoma cells. HT-29 cells exposed to 0.5, 1.0 and 2.0Gy were infected with ,AdCMV-GFP, a replication deficient recombinant adenoviral vector containing a CMV promoter and green fluorescent protein, or ,AdCMV-p53, a replication deficient recombinant adenoviral vector containing a CMV promoter and carrying human wild-type ,p53, gene. Survival rate of the cells was determined by clonogenic assay. Cell cycle and cell apoptosis were determined by flow cytometry. The results showed that, 0.5—1.0Gy irradiation significantly enhanced the inhibition of ,AdCMV-p53, infection on HT-29. Compared with the control, 1day after the infection, the cells in G,0,/G,1, phase decreased by 5%—15%, the cells in S phase increased by 2%—19%. The 0.5 and 1.0Gy irradiation made the cells in the in G,2,/M phase increase by 12%, infected with 80 MOI ,AdCMV-p5,. Three days later, the proportion of cells in G,2,/M phase in groups of 0.5 and 1.0Gy irradiation + 40 MOI ,AdCMV-p53, infection increased by 10%—13%. There was a relation between cell apoptosis and irradiation dose, or ,AdCMV-p53, dose. Therefore, the irradiation-induction could quicken the progression from G,0,/G,1, phase to S phase, and promote S and G,2,/M phase arrest.