Aiming to enhance the positive temperature coefficient (PTC) effect of resistance, immiscible polymer blends [ultra-high molecular weight polyethylene (UHMWPE)/polyvinylidene fluoride (PVDF) ¼ 4 : 1] based composites containing hybrid fillers [carbon nanotubes (CNTs) and carbon black (CB)] were explored. The conductive fillers were premixed with UHMWPE by melt-mixing and then PVDF was introduced into the blends. The preferential distribution of conductive fillers in the UHMWPE phase was desirably observed. Besides decreasing the electrical resistivity of the single UHMWPE based PTC materials, the addition of PVDF with much higher melting point could improve the temperature range of the PTC materials, which is important for their potential applications. A remarkable synergetic effect arising from the combination of CB and CNTs with different geometric structures and aspect ratios on improving the PTC behavior was demonstrated. By introducing 0.5 vol% CNTs into the 4 vol% CB filled UHMWPE0.8-PVDF0.2 composites, the initial resistivity decreased by about two orders of magnitude and the PTC intensity (PTCI) increased by about 30%. Owing to the 3-dimensional conductive networks provided by tube-shaped CNTs and spherical CB and the high viscosity of the UHMWPE matrix, favorable PTC repeatability was also achieved.