For the production of polymer-based conducting composites serving as positive temperature coefficient (PTC) materials with lower room-temperature resistivity and sufficiently high PTC intensity, carbon black has been pretreated. with acrylic acid and some initiator and then melt-mixed with low-density polyethylene. Because of the in situ formation of covalent bonding at the filler/matrix interface, the distribution status and thermally induced displacement habit of the conductive fillers have changed accordingly. As a result, the electrical performance of the composites can be tailored as desired. The amount of acrylic acid and the treatment sequence of carbon black exert an important influence on the effectiveness of the modification.