Electrical and melt rheological properties of melt-mixed polycarbonate (PC) and co-continuous PC/poly(styrene-acrylonitrile) (SAN) blends with carbon nanotubes (CNTs) are investigated. Using two sets of mixing parameters, different states of filler dispersion are obtained. With increasing CNT dispersion, an increase in electrical resistivity near the percolation threshold of PC-CNT composites and (PC+CNT)/SAN blends is observed. This suggests that the higher mixing energies required for better dispersion also result in a more severe reduction of the CNT aspect ratio; this effect was proven by CNT length measurements. Melt rheological studies show higher reinforcing effects for composites with worse dispersion. The Eilers equation, describing the melt viscosity as function of filler content, was used to fit the data and to obtain information about an apparent aspect ratio change, which was in accordance with measured CNT length reduction. Such fitting could be also transferred to the blends and serves for a qualitatively based discussion. (c) 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 79-88