Oyster oligopeptides were prepared by enzymolysis from shelled oyster meat. The molecular weight distribution, DPPH radical scavenging capacity, hydroxyl free radical (·OH) scavenging capacity, ABTS free radical scavenging capacity and oxygen radical absorption capacity (ORAC) of oyster oligopeptides were compared before and after digestion in vitro. The changes of antioxidant activity of the oligopeptides after digestion in simulated stomach and intestine were explored. The experimental results showed that the relative molecular weight of oyster oligopeptides was mainly under 1 000 Da, and the average molecular weight of pepsin and trypsin decreased by no more than 8.2%; after pepsin and trypsin digestion, the DPPH free radical scavenging rate decreased by no more than 7.9% and 8.7%, respectively; after pepsin and trypsin digestion, the ·OH scavenging rate decreased by no more than 9.3% and 3.8%, respectively; after pepsin digestion, and the ABTS free radical scavenging rate decreased by 9.2% and after trypsin digestion, the ABTS free radical scavenging rate increased by 3.6%; after pepsin and trypsin digestion, ORAC increased by 11.5% and 1.3%, respectively. Gastrointestinal digestion had no significant effect on the antioxidant activities of oyster oligopeptide (P＞0.05). The results showed that oyster oligopeptides had good comprehensive antioxidant activity and stability.