Carbon black/polymer composites can be used in a wide variety of applications, such as for antistatic shielding. Some of these applications rely on the enhancement of conductivity that the carbon black filler imparts to the polymer matrix. This study has involved modifying the structure and surface functionality of a high structure (H) carbon black by gasification with carbon dioxide, thereby allowing the properties of the corresponding composite to be modified systematically; Partial gasification of the carbon black decreased the room temperature volume resistivity, at the same concentration (wt %) of carbon black in the composite, and decreased the magnitude of the positive temperature coefficient effect. The results are discussed in terms of a carbon black structure modification and its relation to mechanical and electrical properties.