Abstract: PVDF-HDPE/CB conductive polymer composites were prepared by a two step melt mixing method using poly(vinylidene fluoride) (PVDF) and high density polyethylene (HDPE) as the matrices, carbon black (CB) as the filler. The structures of composites were characterized by Differential Scanning Calorimetry analysis (DSC), solvent extraction and Scanning Electron Microscopy (SEM), respectively. Properties were characterized by electric resistance tester, etc. The relationships between the volume ratio of PVDF to HDPE and the structures of composites were characterized and positive temperature effect (PTC) characteristics and voltage withstanding were also investigated. Results revealed that the compo sites had a biphase PTC structure. In addition, in composites, HDPE could easily form a continuous phase even at a small amount and significantly improve the electrical conductivity and the capability of voltage withstanding of conductive polymer composites.