Carbon fibers (CF) are widely being used in polymer-matrix composites because they have good mechanical, thermal and electrical properties. These properties of carbon fiber are also important to apply to solar cell parts. PP/CF composites was made of polypropylene and carbon fibers whose length are different each other. The mechanical, electrical and thermal properties of these composites are analyzed by thermo gravimetric analysis (TGA), field emission scanning electron microscope (FE-SEM) and universal testing machine (UTM). Finally it can be shown that an increase in fiber length can enhance the thermal stabillity of PP/CF composites and improve the mechanical and electrical properties.