Over the last decades, carbon nanotube (CNT)-filled conductive polymer composites (CPCs) have demonstrated great potential as a highly desired class of advanced functional materials. The CNT content required for achieving the percolation threshold in the CPCs depends on several factors including the type and intrinsic electrical conductivity of the CNTs, the aspect ratio, the degree of alignment, the level of dispersion, and the interconnectivity of the CNTs in the polymeric matrix. Among these parameters, the level of dispersion and the interconnectivity of CNTs have a crucial effect on the electrical conductivity. It is believed that the contact resistance of the conductive network and the dielectric properties of the CPCs can be dramatically altered via slight geometrical changes in the local contact regions between the nanotubes. The current research work is focused on studying the effects of the type and content of polypropylene (PP) crystals on the electrical properties of PP/CNT composites. The isothermal crystallizations of PP/CNT composites were performed at different temperatures (135-150 ºC) under atmospheric and supercritical carbon dioxide (scCO2) conditions. The experimental results indicate that the γ-form of PP crystals was formed under scCO2 atmosphere at elevated temperature. Transformations of the PP crystals, from α-form to γ-form crystals, caused by the differences in the isothermal crystallization conditions, were shown to have remarkable effects on the electrical conductivity and the dielectric properties of the PP/CNT composites.