Abstract: In order to optimize the preparation process of RS₃chestnut resistant starch by acid solution and understand its antioxidant properties,the preparation process from Xinyang chestnut was optimized by orthogonal experiment,and the antioxidant activity of resistant starch was investigated.In single factor experiments,the chestnut suspension mass fraction,hydrochloric acid dosage,acid hydrolysis temperature and acid hydrolysis time were selected respectively,the results showed that the yield of RS₃chestnut resistant starch was higher when the chestnut suspension mass fraction was 20%~30%,hydrochloric acid was 1.0% to 2.0%,the temperature of acid hydrolysis was 35℃ to 45℃ and the time of acid hydrolysis was 2.0 h to 3 h.The orthogonal experiment with 4 factors and 3 levels were employed to explore the optimal extraction ratio of RS₃chestnut resistant starch,the results showed that the yield of RS₃chestnut resistant starch was 8.72% when the chestnut suspension mass fraction and hydrochloric acid was 25% and 1.5% respectively,the temperature and time of acid hydrolysis was 45℃ and 3 h respectively.The antioxidant experiments indicated that RS₃chestnut resistant starch prepared by acid hydrolysis had a good antioxidant activity,the scavenging rate of DPPH was 45.2% by 10 mg/mL RS₃which was equal to a half of 6 mg/mL Vc.The scavenging rate of the superoxide anion free radical was the same as 4 mg/mL Vc,and when the temperature was 60℃,the scavenging rate of nitrite reached the maximum 63.20%.The results also showed that the total antioxidant capacity of RS₃chestnut resistant starch had a good linear relationship with its concentration.