A surface of particles of a silicone resin is treated with a low-molecular organosilicon derivative, with or without a water-soluble cationic polymer to improve the hydrophilicity of the silicone resin. The thus-treated powder is quite excellent in dispersibility (readily dispersible) and in dispersion stability in an aqueous dispersion medium. The use of the surface-treated powder provides a dispersion for cosmetic, excellent in dispersibility and dispersion stability and the like. The use of the surface-treated powder, or the use of the dispersion provides further a cosmetic excellent in dispersibility and dispersion stability, and further excellent in ease of re-dispersion and dispersion stability with lapse of time when selecting aqueous cosmetic as an agent form, and also excellent in smooth feeling in comparison with ordinary products.