Objective: This study aimed to improve the utilization value of scallop processing by-products, by analyzing the antioxidant activity of its protein hydrolysates. Methods: The processing by-products of Argopecten irradians were used as raw materials, and the proteins were extracted by alkali extraction and acid precipitation, alkali extraction and ammonium sulfate precipitation and low temperature ethanol denaturation precipitation. Then the proteins were analyzed by SDS-PAGE. Pepsin, flavourzyme, dispase and alcalase were used to hydrolyze the protein, and the antioxidant activities of the hydrolysate products were analyzed. The molecular weight distribution, amino acid composition and hydroxyproline content of dispase hydrolysates were further analyzed. Results: The purity of protein obtained by alkaline ammonium sulfate precipitation method was the highest, reaching 91.16%, with the optima electrophoretic results. All the four hydrolysates had DPPH, ABTS, hydroxyl radical scavenging ability and reducing ability, and the dispase hydrolysate showed the highest antioxidant ability, especially hydroxyl radical scavenging rate, which reached (77.24±1.87)%. The hydrolysate of dispase contained 15 kinds of amino acids such as aspartic acid, with a total content of 84 g/100 g, and the content of hydroxyproline reached (11.82±0.09)%. Conclusion: The protein obtained from the by-products of scallop processing by alkaline extraction and ammonium sulfate precipitation, and its dispase hydrolysates have optimal antioxidant activity and high nutritional value, which can be further developed as antioxidant functional food.