The effect of the structure of carbon black aggregates on the melt behavior and electrical conductivity of carbon black-vinylchloride-vinylacetate copolymer systems was analyzed. As the amorphous carbon aggregates are roll-milled, they become cylindrical, then, as the milling time is prolonged, spherical. During milling, polymer adsorption and dispersivity increases in the same manner, causing the viscosity of the composite to decrease. It was established that during a certain milling time, conductivity rises to a peak, after which it falls. We attribute this phenomenon to there being an optimum aspect ratio and degree of dispersion of the cylindrical carbon aggregates. A model explaining the relationship between milling time and change in conductivity is proposed. When oxidized carbon black was dispersed into the copolymer, it was found that it disperses better than unoxidized carbon black, although the conductivity of the resulting composite is lower.