This study aims to analyze the reflectivity measurement uncertainty of a spectrophotometer, with considerations of the perpendicular incidence/reflection, scattering, and artificial manipulation. The operation procedure is designed to utilize a double beam spectrophotometric system, taking advantage of the direct comparison of the luminous intensity to evaluate the uncertainty. The environmental range of the temperature and the relative humidity for the measuring process are controlled to be 23 +/- 1.5 degrees C and 50%+/- 10%, respectively. The range for correction reflectivity is 10% - 100%. High-reflectivity standard parts are used with the integrating sphere for the calibration. Low-reflectivity standard parts are used along with an integrating sphere for the evaluation when the measurement reflectivity is 0% - 9%. The optimal expanded composition uncertainty of the system is found to be 1.2% in the wavelength range of 400 nm - 700 nm.
