Among the techniques commonly used, small angle X-ray scattering (SAXS) is, in principle, particularly suited for the analysis of nanostructured systems. However, catalysts supported on porous materials are three phase systems (support, voids and metal), so that the resulting spectrum contains more information than a single conventional SAXS measurement allows to extract. The use of synchrotron radiation source allows to circumvent this difficulty and to separate the scattering of the support from the one of metal by taking advantage of the so-called anomalous or resonant behavior of the atomic scattering amplitude of an element near its absorption edge. The results so far obtained on some Au, Pd and Pd-Au samples supported on active carbon are reported here.