To obtain a modifying carrier suitable for stabilizing a proteolytic enzyme, the proteolytic enzyme chemically modified by the modifying enzyme, and to provide a method for producing the enzyme.

The modifying carrier is a copolymer consisting mainly of an N-alkylacrylamide expressed by formula (1) [wherein, R1, R2 are each H, a 1-8C alkyl, a 3-7C cycloalkyl, a 3-7C aminoalkyl, a 3-5C alkoxyalkyl, tetrahydrofurfuryl, pyrrolidyl or piperidyl; and (m) is an integer of 1-1,000] and maleic acid as monomer components, and when producing the modified enzyme having the proteolytic activity, the carrier is weighed by ≥1.25 mg per 1,000 U/ml enzyme activity value in 1 ml aqueous solution containing the proteolytic enzyme, and the carrier is added into the aqueous solution containing the proteolytic enzyme for a reaction. The modified enzyme thus obtained, receives small effect on the reduction of the enzyme activity by a dialysis treatment or heating, and is excellent in stability.