Phase morphology of melt-mixed polypropylene (PP)/acrylonitrile-butadiene-styrene (ABS) blends was found to be blend ratio dependent, viz., matrix-particle dispersed type of morphology which was observed up to 30 wt% of ABS level beyond which the morphology showed co-continuous type. The domain size of 80/20 PP/ABS blends was found to decrease significantly at 10 wt% carbon black (CB) level, and in case of 70/30 blends morphology was transformed into co-continuous type in the presence of CB, which was retained up to 60 wt% ABS. The finer morphological features were associated with the compatibilizing action of CB particles. Continuous network was achieved through aggregated CB particles predominantly in the PP phase wherein one could find CB-rich PP phase and CB-less PP phase. Solution experiments further supported the existence of CB particles preferentially in the PP phase. AC electrical conductivity measurements indicated a 3D network-like structure of CB aggregates in the co-continuous compositions which showed enhanced electrical conductivity as compared to the matrix-dispersed type of morphology in 80/20 PP/ABS blends which exhibited insulating behavior. On increasing ABS content in the blends the electrical conductivity decreased progressively due to a difficulty in retaining 3D continuous network of CB aggregates especially at 40/60 composition. Increased processing temperature led to a higher electrical conductivity in the respective blends. Dielectric measurements revealed the existence of metallic type of conduction in the co-continuous compositions. However, 80/20 blends showed low epsilon' value. Overall, structure property relationship studies were conducted in PP/ABS blends with CB. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 998-1004, 2009