A method for producing an alkyl-esterified glycosaminoglycan, which comprises the step of allowing a trialkylsilyldiazoalkane to act on a glycosaminoglycan to perform alkyl-esterification of carboxyl groups of the glycosaminoglycan, and an alkyl-esterified glycosaminoglycan having a property that it is not substantially degraded by a glycosaminoglycan degrading enzyme such as hyaluronidase are provided.