Reflectance R, ellipsometric parameters (ψ, Δ), depolarizations , and cross-polarized depolarization of specular reflection, and scattering by a rough stainless steel surface are measured using a null ellipsometer. The three polarization elements of a principal Mueller matrix are obtained from , ψ, and Δ. The measured ψ and Δ of specular reflection for incident angle are fit to the Fresnel equations to obtain n and k. The measured specular is fit to Beckmann’s scattering theory to obtain the root mean square (rms) roughness σ. The fit σ (= 392 nm) is of the same order as the stylus measured σ (= 484 nm). The of specular reflection is small (< 0.07). Scattering measurements are made with variable sample orientation at a detection direction 40 deg backward from the incident direction. The of scattering is very small (< 0.002). The values of ψ, Δ, and of scattering are about constant for an off-specular angle (OSA) within ±60 deg and can be explained by the facet model with single scattering. The measured bidirectional reflectance distribution function (BRDF) in this region can be converted to slope angle distribution with slope angle. The values of ψ, Δ, and of scattering deviate significantly and symmetrically from a constant level for for which the simple facet model with single scattering does not apply. © 2002 Society of Photo-Optical Instrumentation Engineers.