The electrical conductivity of low density polyethylene (LDPE)/carbon black (CB)irradiated by γ ray was investigated at different temperature. The relationship between the PTC and NTC effects was investigated by using scanning electron microscopy (SEM). The radiation dose was shown to have remarkable effects on the positive temperature coefficient (PTC) and negative temperature coefficient(NTC) effects of the composites. An interesting phenomenon was founded that at 400 kGy the NTC effect was nearly eliminated and when the radiation dose raise, the NTC effect reappears. The explanation of this particular behavior was discussed.