The present invention addresses the problem of manufacturing industrially with a simple method without using special equipment that requires a high shear force a purified lactic acid glycolic acid copolymer preferably a powdered purified lactic acid glycolic acid copolymer in which content of dimers such as residual lactide and glycolide is reduced and of manufacturing industrially and simply a highly purified lactic acid glycolic acid copolymer which has a reduced amount of dimers such as residual lactide and glycolide and lactic acid glycolic acid copolymers with a small molecular weight or a salt thereof and which has a small weight average molecular weight/number average molecular weight ratio (Mw/Mn). The present invention manufactures a purified lactic acid glycolic acid copolymer (A2) or a salt thereof with a method that includes the steps of: (1 1) dissolving a lactic acid glycolic acid copolymer (A1) that has a lactic acid unit and a glycolic acid unit or a salt thereof in one type or more of an organic solvent (B1) which has a solubility of 1 weight% or more at 25°C to produce a solution of the lactic acid glycolic acid copolymer (A1) or a salt thereof； (1 2) adding at least one solvent (S1) selected from water and aliphatic alcohol (B2) into the solution of the lactic acid glycolic acid copolymer (A1) or a salt thereof to produce a liquid mixture that includes the lactic acid glycolic acid copolymer (A1) or a salt thereof； (2) adding the liquid mixture produced in the step (1 2) to a solvent (S2 ) that includes at least one selected from water and aliphatic alcohol (B2) to precipitate out the purified lactic acid glycolic acid copolymer (A2) or a salt thereof； and (3) collecting the precipitated purified lactic acid glycolic acid copolymer (A2) or a salt thereof.
