In this study, the survival of cultured Chinese V79 hamster cells irradiated with carbon ions with different LETs were investigated. Irradiation was performed at the Heavy Ion Research Facility in Lanzhou (HIRFL). Results were compared with those obtained from the experiments with ,γ, rays and could be concluded as follows: The survival curves for carbon ions showed as straight lines and were fitted to the one—target one—hit model,but for ,γ, rays the curves with shoulders were fitted to the multi—target one—hit model. As the LETs were 125, 200 and 700keV/μm for carbon ions, the inactivation cross section 35, 12 and 8μm,2, respectively, which suggested that under the experimental conditions, the lower the LET of carbon ions, the more seriously the irradiation killed cells. In the case of 125keV/μm, the RBEs of carbon ions at the 0.1 amd 0.37 survival levels were 1.47 and 2.19 respectively.