Conductive polymer composites (CPC) containing nickel-coated carbon fiber (NiCF) as filler were prepared using ultra-high molecular weight polyethylene (UHMWPE) or its mixture with ethylene-methyl methacrylate (EMMA) as matrix by gelation/crystallization from dilute solution. The electrical conductivity, its temperature dependence, and self-heating properties of the CPC films were investigated as a function of NiCF content and composition of matrix in details. This article reported the first successful result for getting a good positive temperature coefficient (PTC) effect with 9-10 orders of magnitude of PTC intensity for UHMWPE filled with NiCF fillers where the pure UHMWPE was used as matrix. At the same time, it was found that the drastic increase of resistivity occurred in temperature range of 120-200 degrees C, especially in the range of 180-200 degrees C, for the specimens with matrix ratio of UHMWPE and EMMA (UHMWPE/EMMA) of 1/0 and 1/1 (NiCF = 10 vol %). The SEM observation revealed to the difference between the surfaces of NiCF heated at 180 and 200 degrees C. Researches on the self-heating properties of the composites indicated a very high heat transfer for this kind of CPCs. For the 1/1 composite film with 10 vol % NiCF, surface temperature (T-s) reached 125 degrees C within 40 s under direct electric field where the supplied voltage was only 2 V corresponding to the supplied power as 0.9 W. When the supplied voltage was enough high to make T-s beyond the melting point of UHMWPE component, the T-s and its stability of CPC films were greatly influenced by the PTC effect. (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1253-1266, 2009