An inter-relationship between electrical conductivity and microstructure of mechanically mixed dual phase materials was investigated to clarify the conductive mechanism using insoluble systems such as Si SiO₂ and Pb elements. The microstructure of Si/Pb system showed a typical granular structure that Pb particles with a diameter of 0.2㎛ to 5㎛ were dispersed in Si matrix. On the other hand, SiO₂/pb system exhibited a percolation structure that Pb particles with non-uniform shape of sub-㎛ sizes were embedded in amorphous SiO₂ matrix. The morphologies of two mechanically mixed systems were quite different each other. This is believed to be due to the difference of plastic deformability of Si and SiO₂ elements. We also found that no considerable dissolution of Si and SiO₂ into Pb was detected. The two insoluble systems showed a positive TCR(Temperature Coefficient of Resistance) property from 4.2K to 300K and had a same conductor-insulator (semiconductor) transition composition at 15 vol.% of Pb. This can be concluded that the mechanism of electrical conductivity in these systems can be interpreted as a percolation theory. A very high electrical resistivity of these systems is attributed to the percolation structure (clusters) having many links and deadends, and introduced many defects (dislocation, void, vacancy, stacking fault) and internal stress during mechanical mixing process. These factors will interfere with the movement of conductive electrons significantly. The mechanism of electrical conductivity of these systems can be explained by Cayley-tree networks.