To investigate the antioxidant activities of Stichopus japonicus (sea cucumber) proteolysates produced by different proteases, three proteases were exogeneously added to fresh sea cucumber (alkaline protease, neutral protease, and papain). The degree of proteolysis, molecular distribution, and radical scavenging rates (for DPPH∙, O2-∙ and ∙OH) of each protease group were measured. The degree of proteolysis correlated positively with proteolysis time in the protease groups, whereas no significant change occurred in the control group. The degree of proteolysis was highest for neutral protease (19.4%), followed by alkaline protease, and lastly, papain (16.1%). After proteolysis, the number of large molecular-weight fragments decreased while that of <200 u amino acid fragments increased. The highest crude peptide yield (64.2%) was obtained after one hour of proteolysis in the alkaline protease group. Compared to the proteolysates produced by the untreated sample, the proteolysates produced by the samples subjected to proteolysis for up to two hours had significantly increased antioxidant activities, and their antioxidant activities were positively proportional with the proteolysate concentration. In the neutral protease group, a DPPH∙ scavenging rate of 79.64% was achieved with a proteolysate concentration of 5 mg/mL and proteolysis time of 0.5 h. In the alkali protease group, an ∙O2- scavenging rate of 49.58% was achieved with three hours of proteolysis, and the highest ∙OH scavenging rate (21.78%) was achieved with 0.5 h of proteolysis. In summary, the sea cucumber proteolysate produced by neutral protease exhibited the best antioxidant activity among the three exogenous proteases. Further, exogenous protease addition was found to be an effective method for improving the utilization of sea cucumber proteins.