The effect of surface free energy of acetylene black (AB)/high density polyethylene (HDPE) composites on the positive temperature coefficient (PTC) behavior was investigated. The composition was studied in the context of two-liquid contact angle measurements, i.e., deionized water and diiodomethane. From the TGA results of AB/HDPE composites, the thermal stability was found to increase with increasing AB content. The resistivity of AB/HDPE composites greatly increased near the crystalline melting temperature, due to the thermal expansion of HDPE. It was shown that the PTC intensity defined as the ratio of the maximum resistivity ($ ho$ max) to the resistivity at room temperature ($ ho$RT) was largest at 30 wt.% of AB. From the contact angle results, it was proposed that the decreasing in the London dispersive component of the surface free energy induced by interaction between AB surfaces and HDPE chains is an important role in the fabrication of the resulting PTC composites.