Polyethylene (PE) composites filled with carbon black (CB) were prepared using an internal mixer. Several analytical techniques, including rheometry, gel permeation chromatography, electrical conductivity measurements, differential scanning calorimetry, wide-angle X-ray diffraction, and transmission electron microscopy (TEM), were used to reveal the structural variations, thermal degradation, morphological features, and crystallization of the PE/CB conductive composites. It was found that the PE polymer chains were degraded, forming long-chain branching structures after over 30 min of internal mixing. The electrical conduction of the PE/CB composites was determined by the filler content and distribution. The electrical percolation threshold of the PE/CB composites was determined to be between 20 and 30 wt %. The addition of CB had no significant influence on the crystallinity of the PE/CB composites. In contrast, the electron-beam radiation dose had a significant effect on crystallinity. TEM micrographs of the PE/CB composites exhibit a random four-phase morphology, including PE lamellae, PE amorphous, CB particles, and voids at the PE/CB interface. (C) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 1038-1046, 2013