Mirrors with very low-scattering optical surfaces (BRDF <1 x 10-5 sr-1) are being used in military applications. Energy scattered from dust particles on the surface of these mirrors can cause a degradation of the performance of the sensor. A study was made to determine the effect of particle contaminant on the mirror-scattering properties. The study involved contaminating low-scatter mirrors, characterization of the contamination level, and measurement of the Bidirectional Reflectance Distribution Function (BRDF). Comparison of experimental measurements was made with values of BRDF predicted by the Mie particle-scattering theory.