New STS (from solids to sols) technique for studying supported metal catalysts by small angle X-ray scattering without parasitic scattering signal from porous support has been proposed. Due to selective dissolution of support, this parasitic scattering disappears. Efficiency of STS technique was demonstrated on three different supported catalysts. A good agreement between transmission electron microscopy data for initial supported catalysts and small angle X-ray scattering data for sols prepared from them was found. STS technique can be an expansion of small angle X-ray scattering application for analysis of wider range of solid functional materials with poly-phase composition. The main limitation of such technique is possibility of selective dissolution of different phases in complex material.