A keratin hydrolysate including at least 88% by weight of free amino acids relative to the total weight of the amino acids of the hydrolysate, the remainder of the hydrolysate being peptides having a molecular mass of less than or equal to 800 Dalton, the hydrolysate also including L-cystine in a content ranging from 4% to 6%, cysteine in a content of less than or equal to 0.1%, and tyrosine in a content of less than or equal to 0.6% by weight, relative to the total weight of the hydrolysate. Also, a process for preparing the hydrolysate, the oral cosmetic use of the hydrolysate for improving the appearance of the nails and/or of the hair, and a dietary supplement including the hydrolysate and optionally vitamins, zinc and/or L-cystine.
