Providing a method for producing a compound represented by formula (1) from a compound represented by formula (2), by which the additive amount of an aryl (C1-C8) alkyl alcohol which may have a substituent and the amount of residual carboxyl groups of pAsp (polyaspartic acid) are controlled. A production method including obtaining a compound represented by formula (1) by allowing a compound represented by formula (2) to react with an aryl (C1-C8) alkyl alcohol which may have a substituent, and a carbodiimide-based compound in an amount of 2 (x+y) equivalents or more relative to the amount of carboxyl groups in formula (2) (sum of x and y), in a solvent at 15°C to 30°C for 2 hours to 48 hours, is used.
