The bipolar plates are the essential part of Proton Exchange Membrane (PEM) fuel cells made of polymer-based-carbon composite or coated metallic materials. The composite type of bipolar plates has different microstructural and electrical properties that can considerably change under the operating conditions because of exposing to the high body temperature of the fuel cell and flowing the electric current from the parts named joule-heating effect. In this research, the different types of composites, containing phenolic resin as matrix and carbon fiber, graphite, and expanded graphite as filler, have been manufactured. The structural and electrical properties have been investigated by performing the heat-treatment (in three temperatures of 50, 100, and 150°C) and joule-heating effect (in three induced powers 1.5, 5, and 10 W) tests. Here, the effect of time has been investigated too. Finally, SEM and optical microscopes, as well as DSC-TGA, electrical conductivity, and performance analyses are used for characterization. The results of electrical conductivity of different composites in the heat-treatment and joule heating effect tests showed that some of composite have a positive and some of them show negative temperature coefficient of resistivity.