Polymer based PTC (positive temperature coefficient) composites are of special interest since they have great potential in temperature sensitive devices. In order to obtain a reproducible PTC composite with acceptable PTC intensity, the effects of processing conditions and filler treatment with nitric acid and titanate coupling agents on room temperature resistivity, PTC intensity, and melt viscosity of carbon black filled low density polyethylene composites have been described and discussed in the present paper. The results show that interfacial effect is a key factor influencing the processability and ultimate material performance, which can be tailored in various ways.