The present invention relates to a method for producing poly (lactic acid-co-glycolic acid) copolymer particles having an average particle size in the range of 50 to 800 nm, which method comprises the following steps: a) ethanol and monomers to be polymerized A poly (lactic acid-co-glycolic acid) copolymer having a unit content of 55 to 80 mol% lactic acid and 20 to 45 mol% glycolic acid and having a molecular weight Mw of 1,000 to 25,000 B) transporting the carbon dioxide into the first reactor, b) supplying carbon dioxide to the first reactor so that carbon dioxide is 65 to 85 wt% and ethanol is 15 to 35 wt%； Carbon and ethanol total 100%. C) Poly (lactic acid-co-glycolic acid) copolymer, ethanol and carbon dioxide are mixed by stirring. Adjusting or maintaining the mixture in the first reactor at a temperature of at least 31-70 ° C. and a pressure of at least 7.38-50 MPa, d) stirring the mixture from step c) for 1-5 hours E) dissolving at least a portion of the poly (lactic acid-co-glycolic acid) copolymer in a mixture of carbon dioxide and ethanol； e) mixing the mixture from step d) in the second reactor. Transporting to pressure, rapidly reducing pressure, expanding by phase separation to form an ethanol suspension containing gas phase, aerosol and poly (lactic acid-co-glycolic acid) copolymer particles, f) carbon dioxide gas from the reactor And e) removing the ethanol aerosol, g) a poly (lactic acid-co-glycolic acid) copolymer having an average particle size in the range of 50-800 nm Children, comprising a step, obtained from the second reactor or dry form ethanol suspension.本発明は、５０～８００ｎｍの範囲にある平均粒径を有するポリ（乳酸－ｃｏ－グリコール酸）コポリマー粒子を製造する方法に関し、この方法は、以下の工程：ａ）エタノールと、重合されるモノマー単位の含量が５５～８０ｍｏｌ％の乳酸および２０～４５ｍｏｌ％のグリコール酸であり、かつ分子量Ｍｗが１，０００～２５，０００であるポリ（乳酸－ｃｏ－グリコール酸）コポリマーとを、撹拌機器を備える第一の反応器内に輸送する工程、ｂ）二酸化炭素が６５～８５重量％、エタノールが１５～３５重量％になるように二酸化炭素を第一の反応器に供給する工程、ここで二酸化炭素およびエタノールは、合計１００％になる、ｃ）ポリ（乳酸－ｃｏ－グリコール酸）コポリマー、エタノールおよび二酸化炭素を撹拌により混合し、第一の反応器内の混合物を、少なくとも３１～７０℃までの温度および少なくとも７．３８～５０ＭＰａまでの圧力に調整また
