PURPOSE: To produce the titled carrier having a large absorption amount of lysozyme and improved liquid permeability, by crosslinking porous, granular chitosan with a dicarboxylic acid derivative and then acetylating.

CONSTITUTION: Low molecular weight chitosan is dissolved in an aqueous solution of acetic acid, etc., and the solution is dripped to a coabulating bath to prepare porous, granular chitosan. The chitosan is stirred with a dicarboxylic acid derivative in a solvent at normal temperature for 24 hours and crosslinked. An active ester of a dicarboxylic acid, the dicarboxylic acid derivative, such as di-p-nitrophenyl ester, di-N-hydroxysuccin-imide ester, etc., or a dicarboxylic acid halide such as acid chloride, acid bromide, etc., may be used as the crosslinking agent. A compound shown by formula I wherein n is 0W8 is used as the dicarboxylic acid. The crosslinked chitosan is acetylated with an acetylating agent.