Heterogeneous polymer blends filled with conductive filler often show preferential distribution of the filler particles in one of the blends components or at the interface. This phenomenon leads to the lower percolation threshold in comparison with single matrix composites or systems with random filler distribution. In this contribution the rheological and electrical properties of polystyrene/polymethylmethacrylate blends with co-continuous structure and containing different amount of carbon black are discussed. Furthermore, the coarsening of the phase structure during annealing under quiescent conditions in the molten state is evaluated by image analysis of SEM micrographs. It follows from the experiments performed, that the coarsening of the phase structure is suppressed by the appearance of flow restrictions induced by build-up of carbon black particle structures.