This work proposes a novel supercritical assisted process for nanoparticle production, called Supercritical Assisted Injection in a Liquid Antisolvent (SAILA). An expanded liquid solution formed by supercritical carbon dioxide (SC-CO2) and an organic water miscible solvent, is produced, in which a solid solute is solubilized. Then, the solution is depressurized into a water solution in which the solute is not soluble: the water based solution works as a liquid antisolvent and nanoparticles are produced. The process is substantially continuous: the expanded liquid is directly injected in a continuous stirred tank containing a constant volume of water. The process is successful in the production of nanoparticles of polycaprolactone, selected as model compound. The effect of the process parameters on nanoparticle diameter has been studied; it decreases increasing the gas to liquid ratio, the water to solvent flow rate ratio, the saturator temperature and decreasing the polymer concentration. Nanoparticles with a mean diameter down to 64 nm have been obtained. Nanoparticle formation mechanism seems to be guided by the micromixing between the expanded liquid solution and the receiving water solution, followed by nucleation and growth of nanoparticles. The presence of surfactants in the water receiving solution avoids nanoparticles coalescence. (C) 2012 Elsevier B.V. All rights reserved.