Brown algae (Sargassum aemulum) was collected in Khanh Hoa coastal then treated (washing, drying to 19 percent moisture and grinding) and used to extract phlorotannin. The Box Behnken model was applied to design the experiments and to optimize for the technical parameters in the phlorotannin extraction process. The research results showed the optimum condition for phlorotannin extract (included as): extract temperature 48°C, extract time 36 h with the ratio of methanol 80 percent solvent/material (v/w) is 42. The experiment with the about mentioned parameters provided the highest content of phlorotannin as 1.93 mg; total antioxidant activity is 8.11 mg ascorbic acid; reducing power activity is 8.61 mg FeSO4/g dry algae and the smallest content of carbohydrate is 0.3 mg/ g dry algae. The final phlorotannin product with this properties and index can fully be used for food and pharmacy application purpose.