Electret properties of composite polymer materials on the basis of polypropylene were investigated. Investigations were done by methods of thermostimulated and isothermal relaxation of potential and X-ray diffraction analysis. It is shown that aluminium powder adding in pure polymer improves electret stability of original polymer. By a low-angled X-ray dispersion method it was shown that aluminium surface possesses clearly defined fractal properties. Fractal dimensions values indicate that aluminium surface fractions are rough.