Abstract: Free radicals refer to an atom, molecule, or ion that has unpaired valence electrons.Many environmental stimuli, including ultraviolet light, environmental toxins, and hyperthermia, generate high level of free radicals, which leads to cellular oxidative damage.In order to avoid cellular oxidative damage and prevent disease and death caused by oxidative stress, marine organisms develop an effective defense system.The antioxidant system of mollusks includes enzymatic antioxidants such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), thioredoxin peroxidase (TPx), peroxide enzyme (POD), glutathione-S-transferase (GST) and non-enzymatic antioxidants.This article focuses on the research progress of antioxidant enzymes on the sources, distribution and classification as well as the properties, which provides the theoretical basis for its application and prospect.