A process for preparing poly(lactide-co-glycolide) copolymer particles with an average particle size in the range of 50-800 nm includes transferring a mixture of poly(lactide-co-glycolide) copolymer, ethanol and carbon dioxide from a first reactor into a second reactor under rapid reduction of the pressure and expansion with phase separation into a gas phase, an ethanol aerosol and an ethanolic suspension containing poly(lactide-co-glycolide) copolymer particles, removing the carbon dioxide gas and the ethanol aerosol from the second reactor, and obtaining the poly(glycolide-co-lactide) copolymer particles in the form of an ethanolic suspension or in dry form from the second reactor.