PROBLEM TO BE SOLVED: To impart an excellent water-repellency and wear resistance to a protein fiber by reacting the protein fiber or its product with a long chain acylating agent in the presence of a base.
SOLUTION: A water-repellency and a wear resistance are imparted to a protein fiber by treating the protein fiber such as wool and silk or a product such as a woven fabric made of the fiber with 0.1-1 pt.wt., preferably 0.7-0.9 pt.wt. long chain acylating agent of the formula CH3(CH2)nCOCI [(n) is an even number of 10-16], e.g. stearoyl chloride based on 1 pt.wt. protein fiber in a polar organic solvent such as N,N-dimethylformamide capable of swelling the protein fiber in the presence of ≥0.5mol, preferably 1-1.5mol base such as pyridine based on 1mol long chain acylating agent at ≤60°C, preferably ≤55°C to introduce the long chain acyl group into a free amino group and/or hydroxide group included in the protein fiber.