NEW MATERIAL:A compound of formula I (R is aliphatic or aromatic carboxylic acid residue; R' is alkyl; n is 2W200).

EXAMPLE: A stearoyl-silk peptide compound.

USE: A fat-soluble cosmetic.

PROCESS: A silk peptide of formula II is reacted with a carboxylic acid halogenide or formula III (X is Cl or Br) in an alkaline solution, e.g. NaOH, at 40W80°C. The reaction solution is then acidified to remove the unreacted silk peptide and solvent by the filtration to afford the compound of formula I. The resultant compound of formula I will dissolve well in various vegetable oils, mineral oils and various esters of fatty acids and further in esters of higher fatty acids, e.g. stearic acid or palmitic acid. The coloring tendency is remarkably reduced, and the stability is improved. The skin beautifying and whitening effect can be expected by the sufficient inhibitory action on tyrosinase activity.