The purpose of the present study was to investigate the effect of the surface properties of silica particles on the classification performance of a dry-cyclone. As a result, it was clear that the separation force between the surface of particle and the silicon was decreased by the AFM measurement when the surface of the silica particles could be modified with ethanol or acetone treatment. Fine particles in the original silica particles with the treatments were easily collected by the filter in a dry-cyclone system; hence, the particle classification performance was enhanced.