Abstract: Intergranular mullite microcrystals have been obtained through adjusting the mole ratio of Al₂O₃/SiO₂. It shows comparatively strong solubility to Fe₂O₃, MgO and other foreign substances. Therefore the borrier potential of crystallite can be lowered, and the desired effect of lowering specific resistance can be brought about. In addition, the relationship between quench temperature and specific resistance and the positive temperature coefficient (PTC dffect at) room-temperature has been presented. As well a proper sintering technique for producing PTC material with low specific resistance has been confirmed and a sample product with low resistivity of 121.1Ω·cm at room-temperature, with R_max/R_20℃ of 2.3 ×10³, has been developed.