To obtain a modified powder which is useful for obtaining a cosmetic which is excellent in conformability to skin, touch feeling and dispersibility by treating the surface of powder particles with a specific compound originating from silk.

Powder particles are treated, on their surfaces, with a treating agent selected from one kind or two or more kinds of N-acylated silk peptides or their salts. The treating agent is suitably an N-acylated silk peptide or its salt prepared by acylating a hydrolyzate of silk fibroin. This modified powder is prepared, for example, by forming a slurry comprising the powder, the N- acylated silk peptide sodium salt and water, adjusting the pH of the slurry to ≤5 with hydrochloric acid thereby forming a coating layer of the N-acylated silk peptide on the surface of the particles. The amount of the modified powder to be added to a cosmetic is about 0.01-99.5wt.%, particularly 0.5-90wt.%.