A new technique STS (from solids to sols) for study of supported metal catalysts by Dynamic Light Scattering (DLS) has been proposed. This technique has been tested on a set of supported gold catalysts with wide range of metal particle sizes. We have prepared a set of Au/Al2O3 catalysts and previously studied them by TEM and XRD. Then using STS technique Au-containing sols were prepared from these catalysts. These Au-containing sols were subsequently studied by UV–Vis spectroscopy and DLS. We found that sizes of gold nanoparticles in initial solid catalysts and in sols prepared from them have similar sizes. Thereby, the possibility of determination of particle sizes in supported metal catalysts using more simple, sensitive and quick methods was demonstrated in this work.