This paper show that the research results about antioxidant phlorotannin distribution and accumulation of 5 brown algae species (S. polycystum, S. serratum, S. mcclurei, S. binderi, S. oligocystum), Those 5 seaweed species were collected from 1/2011 - 4/2011 on the growth time at Lo river - Nha Trang city, Khanh Hoa province. The methods were collected to assay antioxidant activity as total antioxidant, reducing power and DPPH radical scavenging. The result showed that 5 species were performed antioxidant activity by 3 aforesaid assay methods, inside the best reducing power. The experiment showed that phlorotannin distribution and accumulation on the growth time are similar alginate distribution and accumulation in seaweed and accord with researchs that research on brown algae harvest time in Vietnam and on the world.