Abstract: Using the gonad of Sepia lycidas as raw material,optimization of extraction polysaccharides process was studied by using Box- Behnken design based on the results of single- factor test; antioxidant activity of polysaccharides was evaluated by its superoxide anion and hydroxyl free radical scavenging abilities.The results showed that the optimal extraction parameters were as follows: 1∶30g / m L for ratio of raw material to water,90℃ for extraction temperature,and 1h for extraction time. Under the optimal conditions,the extraction rate of polysaccharides was 0.751%.The polysaccharides had good abilities to scavenge hydroxyl and superoxide anion free radical.It was indicated to a positive correlation with concentration of polysaccharides. IR spectrum showed that the polysaccharide was pyranoid glucan with β- glycosidic bond.