Abstract: In order to explore the process optimization and antioxidant activity in vitro of protein extraction from citrus peel byalkali-solution and acid-isolation. The single factor experiments and response surface methodology (Box-Behnken) were combined to optimize the extraction process of citrus peel protein. V_C was used as the positive control to investigate the scavenging effect of the citrus peel protein on DPPH·, H₂O₂, ·OH and \rmNO_2^- . The results showed that the optimum extraction conditions of citrus peel protein by alkali-solution and acid-isolation were as follows: pH12.1, extraction temperature 52.8 ℃, extraction time 2.6 h, solid-liquid ratio 1:42 (g/mL). Under these conditions, the protein extraction rate of citrus peel was 62.23%±0.22%, which was close to the predicted value of regression model (63.01%), showing the good fitting degree. The protein prepared by the optimized process also had good antioxidant activity in vitro, and the half inhibitory concentration (IC₅₀) for scavenging of DPPH·, H₂O₂, ·OH and \rmNO_2^- of citrus peel protein were 1.20312, 0.52516, 0.79207, 0.87216 mg/mL. In summary, the extraction of citrus peel protein by alkali-solution and acid-isolation could provide a way for the resource utilization of citrus peel, and the citrus peel protein had good antioxidant activity and utilization prospect.