A method for purifying a polyethylene glycol compound having one amino group, which includes (A) preparing an aqueous solution of the compound having a pH of 1 to 5, (B) an extracting step of mixing the aqueous solution with a mixed organic solvent to cause layer separation into organic and aqueous layers, wherein a ratio of an organic solvent I is 25 to 65% by mass and a ratio of an organic solvent II is 75 to 35% by mass, the organic solvent I is selected from an aromatic hydrocarbon and an ester, the organic solvent II is a halogenated hydrocarbon, and a mixing ratio Y of I to II, temperature T (° C.) at mixing, and molecular weight M of the compound satisfy the following relationship: 1.9×10−6M+0.09≦Y−0.015T≦−1.4×10−6M+0.44 and (C) recovering the compound from the aqueous layer.