In this study, the influence of the accelerated argon cluster ion beam on the topography of stainless steel and optical glass surfaces has been investigated. The possibility of smoothing the material's surface to the sub-nanometer level of roughness is shown. The dose dependencies of the root-mean-square roughness and power spectral density function are obtained. It is demonstrated that by the cluster ion treatment the effective roughness decreases at different ranges of spatial frequencies. Anisotropic structure of the treated material effects on the obtained surface roughness.