The process of lipid oxidation in fresh and fried oysters during in vitro digestion and the relationship between the antioxidant ability of phenolic esters with different chain lengths were investigated through co-digestion of fresh and fried oysters with gallic acid (GA) and its alkyl esters. Lipid oxidation in fresh and fried oysters during simulated digestion in vitro was observed according to increased conjugated diene value, conjugated triene value, thiobarbituric acid reactive substances and fluorescence intensity of aldehydes. Lipid oxidation in oysters was inhibited by GA and its alkyl esters during in vitro digestion effectively. As the alkyl chain length increased, the antioxidant effect first increased and then decreased, and butyl gallate achieved the highest effect among the GA and its alkyl esters we studied, which suggests that the antioxidant efficiency of GA and its alkyl esters in the digestive system may follow the 'cut-off' effect.