It was well established that microwave radiation was utilized initially to enhance the electrical conductivity of polymer nanocomposites (PNCs) introduced in carbon nanotubes (CNTs) without solvent involved. High electrical conductivity was obtained in Polypropylene (PP) nanocomposites with low carbon nanotubes (CNTs) loading levels. Under inert gas protection, the CNTs were heated through the transformation of electromagnetic energy into mechanical vibrations. The surface of PP was easily molten by the heat generated in CNTs, then a well-formed CNTs network was built under proper microwave treatment period and subsequent hot pressing. CNTs loading levels and processing temperatures play an important role in crystal structure, crystalline fraction and crystallization temperature of both nest PP and its PP/CNT PNCs. Moreover, the pressing temperature and CNT loading levels have an obvious effect on electrical conductivity, which are main factors on network formation. Electron transport with three-dimensional route was observed from the study of the variable range hopping (VRH) mechanistic. The unique negative magnetoresistance (MR) phenomena was shown in the PNCs and theoretically discussed by forward interference model. The calculated optical band gap of PNCs decreased with increasing CNT loadings. Other properties have been also well tested and analyzed.