Abstract: To investigate the antioxidant activity in vitro of enzymatic hydrolysis derived from oyster protein (EHOP for short) by neutral protease, Effects of pre-treatment methods, enzyme addition, pH, temperature and time on extraction result were studied and then the amino acid components and the distribution of the relative molecular weight of EHOP were analyzed. Results showed that the content of peptides obtained through the digestive action could be increased by the pre-treatment methods heated at 100℃ for 10min. These optimized conditions were as follows:E/S 2.0%, pH7.0, temperature 50℃, enzymatic hydrolysis time 3.0h, under which the DH was 14.95%. The EHOP was rich in bioactive peptides and most of the molecular weights were about from 500 to 3091u. They had good ability to eliminate the superoxide anion free radical and ·OH, the scavenging rates of which were shown to be 68.86% and 21.20% respectively when the concentration was 25mg/mL, and the absorption values A 700 was 0.44, which showed strong reducing power.