In this study, free radical scavengers and angiotensin I converting enzyme (ACE) inhibitors from the gelatin hyrdolysates of duck skin by-products were examined. Gelatin was obtained by pretreating duck skin by-products with acid and alkaline and hydrolysis using nine proteases (Alcalase, Collaganase. Flavourzyme. Neutrase, Protamex. papain, pepsin, trypsin and alpha-chymotrypsin). Of the various hydrolysates produced, the pepsin hydrolysate exhibited the highest free radical scavenging activity. The DPPH, hydroxyl and alkyl radical scavenging activity of pepsin was the most prominent with IC50 values of 1.230, 0.554 and 1.193 mg/ml respectively, which were measured using an electron spin resonance (ESR) spectrometer. However, when the gelatin was hydrolyzed as a combination of two enzymes, Collaganase and pepsin, the DPPH, hydroxyl and alkyl radical scavenging activity increased as the IC50 decreased to 0.632, 0.222 and 0.708 mg/ml, respectively. In addition, the ability of pepsin hydrolysates from the gelatin of duck skin by-products to inhibit oxidative damage to DNA was assessed in vitro by measuring the conversion of supercoiled pBR322 plasmid DNA to the open circular form. The enzymatic hydrolysates from the gelatin of duck skin by-products significantly protected hydroxyl radical-induced DNA damage in a dose-dependent manner, while also inhibiting the ACE activity of the alpha-chymotrypsin hydrolysates. These results indicate that enzymatic hydrolysates from the gelatin of duck skin by-products may be a beneficial ingredient in functional foods and/or pharmaceuticals. Published by Elsevier Ltd.