To investigate the changes in telomerase expression and its activity in A549 and L02 cells and their association with apoptosis after exposure of the cells to radiation, the hTERT expression and apoptosis occurrence in the cells by ,in situ, telomerase−apoptosis double staining and the telomerase activity by TRAP were assayed. It is found that from 24—72h after exposure to 1—5 Gy γ−rays, the two cell lines showed a stronger hTERT expression, and the numbers of positive cells in telomerase−apoptosis double staining increased in a dose−dependent manner. Meanwhile telomerase activity in the cells of the two lines was upregulated dose−dependently during the development of apoptosis. The results suggested that the telomerase suppression might not be involved in the radiation−induced cell apoptosis and that telomerase may be related to chromosomal repair.