Abstract: Oat bran protein was extracted by alkaline solution and acid precipitation method. The content of polypeptide was used as evaluation index to screen the most suitable enzyme. The enzymatic hydrolysis conditions of oat bran hydrolysate were determined by single factor and response surface optimization experiments. Oat bran hydrolysates were separated by ultrafiltration, the antioxidant activity of each fraction was determined, and the strongest fraction was selected for animal experiments. In this paper, the aging mouse model was induced by D-galactose (D-gal), and the antioxidant enzyme activities in serum and brain tissue of mice were determined to explore the antioxidant capacity of oat bran hydrolysate. The results showed that alcalase was the most suitable protease, and the optimal conditions were: enzyme addition 15000 U/g, enzyme time 2.5 h, enzyme temperature 53 ℃, enzyme pH9.6, and with peptide content 13.75±0.51 mg/mL. After ultrafiltration, oat bran hydrolysate with molecular weight >10 kDa had the highest antioxidant activity, and the scavenging capacity of DPPH· and ABTS^＋· and the reduction capacity of ferric ion were 19.83±0.15, 868.57±87.01 µmol Trolox/g and 21.36±0.35 µmol/L respectively at the concentration of 10 mg/mL. Compared with the normal group, the SOD, GSH-Px, and CAT activities in serum were significantly reduced and MDA content was significantly increased in the model group (P<0.01). Compared with the aging model group, after intragastric administration of low, medium, and high doses of oat bran hydrolysates, GSH-Px and CAT activity in the serum and brain were significantly increased, significantly increased the activity of SOD in the serum, and the MDA content in aging mice was significantly reduced (P<0.05). The oat bran hydrolysates had good antioxidant activity in vivo and in vitro.