To date, various delivery systems have been developed to improve chemical stability and increase the bioavailability of polyphenolic compounds. In the present study, the micronization of two flavonoids, quercetin and rutin, and their coprecipitation with polyvinylpyrrolidone (PVP) were studied using the supercritical antisolvent process (SAS). SAS process parameters were optimized with the aim of obtaining composite microspheres with controlled mean size and particle size distribution. Spherical microparticles (with mean diameters in the range between 0.47 and 9.52 mu m for PVP/quercetin and in the range 0.84-8.17 mu m for PVP/rutin) were precipitated, depending on the operating conditions. In correspondence of the best operating conditions, the entrapment efficiency in PVP, for both flavonoids, was 99.8% and the dissolution rate from the coprecipitated powders was 10 and 3.19 times faster compared to the dissolution rates of unprocessed flavonoids for quercetin and rutin, respectively.