A process and an apparatus are proposed to perform the supercritical assisted atomization of nano and/or micro metric powders. It is possible to use liquid solvent at process conditions in which they show a low solubility in carbon dioxide. Atomization is obtained by solubilizing pressurized carbon dioxide (compressed, liquid, supercritical) in a solution formed by the solid to be micronized and the liquid solvent, solubilizing carbon dioxide up to near equilibrium conditions and then atomizing the solution down to near atmospheric conditions through a thin wall injector, to produce very small droplet of micronic and sub-micronic dimensions. The subsequent evaporation of the droplets produces particles with diameters ranging between 0.02 and 10 micron.