PURPOSE: To obtain a plaster for poultice having excellent adhesion and shape retention as well as high safety, by using a reaction product of a protein having amino groups on side chains and a (meth)aclylic acid polyalkylene glycol diester.

CONSTITUTION: A gelling retardant such as calcium chloride, urea, etc., is added to an aqueous solution of a protein (e.g. gelatin, proteose, etc.) having amino groups on side chains. An aqueous solution of a (meth)aclylic acid polyalkylene glycol diester expressed by the formula (X is H or methyl; A is oxyethylene or oxypropylene; m is 1W3,000) is added to the protein solution containing the gelling retardant to subject the protein having amino groups on the side chains to partial crosslinking. The resultant reaction product is used as the aimed plaster for poultice. The plaster is able to keep strong adhesive property even after evaporating water content in the plaster, by blending a hydrophlic tackifier (e.g. glycerin or ethylene glycol) into the plaster.