Process for preparing poly(lactide-co-glycolide) copolymer particles with an average particle size in the range of 50 - 800 nm comprising the steps: a) transfer of ethanol and a poly(lactide-co-glycolide) copolymer with a content of polymerized monomer units of 55 - 80 mol% lactide and 20 to 45 mol% of glycolide and a molecular weight M w of 1.000 - 25.000 into a first reactor with a stirring equipment, b) feeding carbon dioxide into the first reactor so that carbon dioxide is from 65 to 85 % by weight and the ethanol is 15 to 35 % by weight whereby carbon dioxide and ethanol add up to 100%, c) mixing the poly(lactide-co-glycolide) copolymer, the ethanol and the carbon dioxide by stirring and adjusting or maintaining the mixture in the first reactor to a temperature of at least 31 and up to 70 °C and a pressure of at least 7.38 and up to 50 MPa, where carbon dioxide enters the supercritical stage with ethanol as a co-solvent, d) stirring the mixture from step c) for 1 to 5 hours, whereby at least a part of the poly(glycolide-co-lactide) copolymer becomes dissolved in the mixture of carbon dioxide and ethanol, e) transfer of the mixture from step d) into a second reactor under rapid reduction of the pressure and expansion with phase separation into a gas phase, an aerosol and an ethanolic suspension containing poly(lactide-co-glycolide) copolymer particles, f) removal of the carbon dioxide gas and the ethanol aerosol from the second reactor g) obtaining the poly(glycolide-co-lactide) copolymer particles with an average particle size in the range of 50 - 800 nm in the form of an ethanolic suspension or in dry form from the second reactor, wherein the average particle size and the molecular weight M w are determined as described herein. a) transfer of ethanol and a poly(lactide-co-glycolide) copolymer with a content of polymerized monomer units of 55 - 80 mol% lactide and 20 to 45 mol% of glycolide and a molecular weight M w of 1.000 - 25.000 into a first reactor with a stirring equipment, b) feeding carbon dioxide into the first reactor so that carbon dioxide is from 65 to 85 % by weight and the ethanol is 15 to 35 % by weight whereby carbon dioxide and ethanol add up to 100%, c) mixing the poly(lactide-co-glycolide) copolymer, the ethanol and the carbon dioxide by stirring and adjusting or maintaining the mixture in the first reactor to a temperature of at least 31 and up to 70 °C and a pressure of at least 7.38 and up to 50 MPa, where carbon dioxide enters the supercritical stage with ethanol as a co-solvent, d) stirring the mixture from step c) for 1 to 5 hours, whereby at least a part of the poly(glycolide-co-lactide) copolymer becomes dissolved in the mixture of carbon dioxide and ethanol, e) transfer of the mixture from step d) into a second reactor under rapid reduction of the pressure and expansion with phase separation into a gas phase, an aerosol and an ethanolic suspension containing poly(lactide-co-glycolide) copolymer particles, f) removal of the carbon dioxide gas and the ethanol aerosol from the second reactor g) obtaining the poly(glycolide-co-lactide) copolymer particles with an average particle size in the range of 50 - 800 nm in the form of an ethanolic suspension or in dry form from the second reactor, wherein the average particle size and the molecular weight M w are determined as described herein.