The polarization characteristics of light scattered by several materials such as paint, metal, dielectric layers are significant. The Stokes-Mueller formalism is used to study the depolarizing properties of sample. The Mueller matrix measurement is introduced. The polarized light from a He-Ne laser ( nm) is used, which is focused onto the surface of the sample, passed through the polarization-analysis optics onto a CCD camera. The retardation plates are submitted to a calibration procedure, 64 images are digitized and a generalized linear least square fit is calculated. The horizontal or vertical polarization, linear 45 or 135 polarization, and right or left circular polarization are compared and analyzed. The results show that for alumiunum plate, circular states have greater depolarization than linear states.