Electrical conductive PVC and HDPE composites were prepared by melt compounding method with electrical conductive carbon black. The electrical and mechanical properties of carbon black composites were affected by the particle size, surface area, density, aggregation morphology and dispersion state of carbon black, According to the carbon black contents, the composites have shown the behaviors of insulator, semiconductor and conductor. The percolation threshold of the carbon black composite was examined. From the temperature dependence of conductivity for the composites, we found that Carbon Black-PVC composites were very stable and reproducible to the temperature changes. Carbon Slack-HDPE composites have shown a PTC(positive temperature coefficient of resistively) effect which has a sudden resistively increase by thermal expansion of polymer at melting region. To prevent a NTC(negative temperature coefficient of resistively) effect and improve reproducibility of conductivity, the chemical crosslinking was accomplished.