The present study was performed to evaluate combination effect of 7$eta$-hydroxycholesterol (7$eta$-OHC) and $gamma$-radiation in NCI-H460 human lung cancer cells. 7$eta$-OHC in combination with $gamma$-irradiation has an enhanced effect in decreasing clonogenic survival and increasing cellular DNA damage. Pretreatment of cells with 7$eta$-OHC enhanced radiation-induced apoptosis. Apoptosis of the cells by combined treatment of 7$eta$-OHC and $gamma$-irradiation was associated with reactive oxygen species generation and loss of mitochondrial membrane potential, resulting in the activation of caspase 9 and caspase 3. The combined treatment also resulted in an increased G1 cell cycle distribution. These results indicate that 7$eta$-OHC shows the additive effect of radiation sensitivity in human lung carcinoma cells in vitro.