In this study, the characterization of a concentrator photovoltaic (CPV) system based on a Cassegraintype optic is presented. The indoor and outdoor electrical parameters have been measured and analyzed. On the basis of the IEC 60891 standard, the acquired I-V characteristics have been reported under the CSTC defined in the CEI 82-25 and the electrical parameters deviations have been determined. The correlations among temperature, direct normal irradiance (DNI) and power have been discussed. The results of the absolute power test based on the ASTM E2527 standard and the values of power deviation are reported. Finally the rating power comparison between the two standard test procedures is performed