PURPOSE: Silk fibroin that is made by bonding N,N-dialkylaminoethyl methacrylate to silk fibroin or regenerated one, thus being used in paints, cosmetics and food products, because of its high pigment adsorption, moisture retention and smell retention.

CONSTITUTION: N,N-dialkylaminoethyl methacrylate of the formula (R1, R2 are alkyl) or a copolymer containing the same as the major component is made to react with a suspension of silk fibroin, preferably of fine particles of 0.1W100 microns particle sizes, or regenerated silk fibroin containing more than 50wt% hot water-insoluble fibroin (β-type) with an average molecular weight of more than 50,000 and a crystallinity of more than 10%, by 0.5W100wt% in the presence of a radical polymerization catalyst such as ammonium persulfate by 0.1W 10wt% based on the above methacrylate at 30W100°C under stirring.