The current concerns of sustainable development make the biobased polymers the object of many studies. Chitosan is a biobased, biocompatible and biodegradable polysaccharide with antibacterial and cytocompatible properties. In this study, we aimed to generate chitosan particles with two processes using CO2 under pressure, in order to decrease the use of organic solvent and to obtain nanoparticles. The first is a supercritical anti-solvent process: CO2 acts as an anti-solvent toward an acetic acid aqueous solution of dissolved chitosan in which ethanol was added to enhance the anti-solvent effect. The reciprocal miscibility of CO2 with the solvents induces the reduction of their solvating power, leading to supersaturation at the capillary outlet and causing the crystallization of the particles. This process led to the generation of more or less agglomerated chitosan nanoparticles with an individual average size of 378 nm. In the second process, the pressurized CO2 is dissolved in water to lower the pH. This in turn allows the chitosan to be dissolved and the resulting solution is sprayed, thanks to the pressurized CO2, into a hot air stream. This new process allowed the generation of dried chitosan nanoparticles with a median size of 390 nm. (C) 2014 Elsevier B.V. All rights reserved.