To investigate the mechanism that AZD7762 reducing cisplatin-mediated G2/M cell cycle arrest in the human osteosarcoma cell lines HOS and Saos-2 cells, the protein of p-Chk1, p-Cdc25c, p-Cdc2, p-histone H2A.X and Cyclin-B1 that involved in G2/M cell cycle regulation were performed in western blot experiments. The gene discussed is H2AX; the disease is osteosarcoma.