Quercetin is a strong naturally occurring antioxidant that is exploited in pharmaceutical and cosmetics applications. Unfortunately, quercetin is highly susceptible to oxidation. Besides, its poor solubility in water and low bioavailability upon oral administration limit the use in drug formulations for the treatment of human diseases. In an effort to overcome these drawbacks, the micronization and coprecipitation of quercetin particles with a low-cost biocompatible polymer (ethyl cellulose, EC) was studied by using supercritical anti-solvent process (SAS) with a non-toxic solvent ethyl acetate. The results showed that SAS micronization of quercetin led to a reduction in the quercetin particle size and crystallinity without a change in the needle-like habit. SAS coprecipitation of quercetin with EC at moderate pressure and temperature (10 MPa and 35 degrees C) led to obtaining quasi-spherical particles. The coated polymer avoid the growth of quercetin crystals, thus amorphous particles in the submicron range (mean size ranging between 150 and 350 nm) were formed. Promising coprecipitation results were reached with quite high process yields (above 85%) and encapsulation efficiencies up to 99% that provided a high stability to the coated quercetin with EC against oxidation. (C) 2015 Elsevier B.V. All rights reserved.