Dry stratum corneum was soaked in aqueous solutions of sodium hyaluronate and sodium acetyl hyaluronate. A specific amount of water was added on the atratum corneum, and then the amount of bound water in the stratum corneum was measured using a differential scanning calorimeter. Sodium acetyl hyaluronate shows a remarkable water retentivity on the skin, holding approximately double amount of water, in comparison with non-acetylated one.