The effects of elastomer and carbon black contents on the positive temperature coefficient(PTC) and the negative temperature coefficient(NTC) behavior of carbon black (CB)-filled HDPE composites are studied. The 20~50wt% CB-filled HDPE composites containing 0, 1, 3 and 5wt％ elastomer are prepared using an internal mixer and compression-molded at 18$0^{circ}C$ for 10min. The PTC/NTC behavior of the composites is dependent on the CB and elastomer contents. The PTC behavior is due to the breakage of the conductive networks, caused by the thermal expansion at the melting temperature of HDPE and the NTC behavior is caused by reformation of conductive chains, resulting from the relaxation of polymer structure and reagglomeration of CB particles. It is found that the impact strength of the composites containing elastomer is improved, even though they exhibit slight decrease in PTC intensity. This probably resulted from the improvement of impact damping, due to the increase in the internal stress of the composites.