Potentially lethal damage repair (PLDR) in HFL-I was investigated by delayed plating experiments. The surviving fraction data were fitted to the linear Quadratic equation (LogSn=-nγ(αd+βd2) where γ=1 for immediate plating). And a repair factor γ was developed to compare survival for immediate and delayed plating . When we only took into account the repair factor of PLDR γ which was derived from the delay assay, the cell survival response th fractionated carbon ion irradiation was not fully matched. This gap suggested that consideration of another repair process is necessary. So this suggests that the various repair process plays an important role in the fractionated irradiations.