A combined cavity ring-down (CRD) and spectrophotometry technique is developed to measure with sufficiently high accuracy the reflectance of any practically fabricated optical laser component with reflectance ranging from below 0.01% to over 99.999%. In this combined technique, a CRD configuration is employed to measure reflectance higher than 99%, and a conventional spectrophotometric configuration, which is formed by simply removing the rear cavity mirror from the CRD configuration, is applied to measure reflectance below 99%. Uncertainties below 0.0001% for reflectance over 99.99% and below 0.3% for reflectance below 99% are experimentally achieved with CRD and spectrophotometry configurations, respectively, of one single experimental setup.