It is an object of the present invention to provide a purified lactic acid-glycolic acid copolymer reduced in dimer content such as residual lactide, glycolide, preferably purified powdery refinement, without using special equipment requiring high shearing force It is an object of the present invention to produce a lactic acid-glycolic acid copolymer industrially and in a simple manner, and to provide a lactic acid-glycolic acid copolymer or a salt thereof in which the amount of residual lactide, a dimer such as glycolide, It is an object of the present invention to industrially and easily produce a lactic acid-glycolic acid copolymer having a high purification degree with a small ratio (Mw / Mn) of weight average molecular weight / number average molecular weight. In the present invention, (1) a lactic acid-glycolic acid copolymer (A1) having a lactic acid unit and a glycolic acid unit or a salt thereof is dissolved in one or more kinds of organic solvents having a solubility of 1% (B1) to prepare a solution of lactic acid-glycolic acid copolymer (A1) or a salt thereof,(1-2) At least one solvent (S1) selected from water and an aliphatic alcohol (B2) is added to a solution of the lactic acid-glycolic acid copolymer (A1) or a salt thereof to obtain lactic acid-glycolic acid A step of preparing a mixed solution containing the copolymer (A1) or a salt thereof,(2) The mixed solution prepared in the step (1-2) is added to a solvent (S2 ) containing at least one selected from water and an aliphatic alcohol (B2), and purified lactic acid-glycolic acid A step of precipitating the copolymer (A2) or a salt thereof, and(3) a step of recovering the purified lactic acid-glycolic acid copolymer (A2) precipitated or a salt thereof,To prepare a purified lactic acid-glycolic acid copolymer (A2) or a salt thereof.本発明は、高せん断力を要する特殊な機器を用いることなく、残留ラクタイド、グリコライドのような二量体の含有量が低減された精製乳酸―グリコール酸共重合体、好ましくは粉末状の精製乳酸―グリコール酸共重合体を工業的に簡便な方法で製造すること、また、残留ラクタイド、グリコライドのような二量体、および分子量の小さい乳酸-グリコール酸共重合体またはその塩の
