Objective:To study the changes of PTEN gene expression in radiationinduced bystander cells.Methods: The irradiated cells and nonirradiated cells were cocultured in a ratio of 11.The culture medium of irradiated cells was used to culture nonirradiated cells to create two bystander cell models. The expression of PTEN mRNA and protein in the bystander cells,irradiated cells,nonirradiated cells was compared.Results: The protein expression of PTEN in the irradiated cells was negatively associated with the irradiation dose.The downregulation degree of PTEN protein was related to the different treatments of cells.The most prominent downregulation was found in the bystander cells cultured with medium of irradiated cells.The downregulation of PTEN protein in the two kinds of bystander cells was more severe than that in the irradiated cells(P<0.01).Conclusion: PTEN protein expression can be influenced by low dose radiation and the bystander effect of radiation.