Survival curves of Chinese hamster V79 cells exposed to accelerated carbon ions with linear energy transfers (LET) of 125.5, 200 and 700keV/,µ,m were measured, respectively. Inactivation cross sections corresponding to the irradiation above were deduced from the survival curves of exposed V79 cells. They are 7.86±0.17, 10.44±1.11 and 32.32±3.58,µ,m,2, respectively in turn. With the survival response of V79 cells to ,60,Co γ rays as a reference value, relatively biological effectiveness (RBE) at 10%, 20%, 50% and 80% survival levels were given for the carbon ions. The results show that carbon ions with LET of 125.5keV/,µ,m have higher values of RBE at any survival levels than others. It prompted that the maximum value of RBE for V79 cell surviving as the biological endpoint appears at the LET below 200 keV/,µ,m for carbon ions.