We report a detailed investigation on the effect of carbon black (CB) morphology on network formation and evolution in high-density polyethylene/CB composites. There were three types of networks in our study, the electrical network in the solid state and the electrical and rheological networks in the melt state. The evolution of the network in the polymer melt was traced by simultaneous electrical resistivity (R) and dynamic rheology testing. An oscillation strain sweep was used to investigate the network stability with a large strain. We found that with high-structure CB with a branched morphology, it was easier to form a filler–polymer or filler–filler network than with low-structure CB with a spherical morphology in the composite melt. The high-structure CB network was more stable with a large strain compared to the low-structure one. Meanwhile, the low-structure CB aggregates had stronger capability of movement and re-aggregation in the polymer melt. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 39953.