The electrical-resistivity/temperature behaviors of low-density polyethylene (LDPE)/carbon black (CB) composites irradiated with Co-60 gamma rays were studied. The experimental results showed that the irradiated composites could be separated into insoluble crosslinking networks with CB (gel) and soluble components (sol) by solvent-extraction techniques. When the sol of an irradiated LDPE/CB composite was extracted, the electrical conductivity of the system increased. The positive-temperature-coefficient (PTC) and negative-temperature-coefficient (NTC) intensities of the gels of the irradiated composites became extremely small and independent of the radiation dose. The sols and gels of the irradiated LDPE/CB composites, which had different thermal behaviors, played important roles in the appearances of the PTC and NTC effects. (C) 2004 Wiley Periodicals, Inc.