A more accurate methodology to measure the reflectance of optical disks, taking into consideration the scattering losses at the surfaces of the disk, is proposed by the National Institute of Standards and Technology (NIST). The proposed method is a modification of the current standard, as described in Annex D of the Standard ECMA-267, second edition, for 120-mm DVD—Read-Only Disk (Dec. 1999, http:/www.ecma.ch/). The experiment shows that the optical losses could be, in some cases, as much as 2% of the incident light power. By accounting for the losses, as in the proposed method, the accuracy of the measured reflectance is significantly improved. Thus, the primary reference disks produced with this method have a higher accuracy in reflectance measurement for the use of optical disk industry.