The influence of sulfated polysaccharide from brown seaweed Laminaria Japonica(SPS) on the respiratory burst of polymorphonuclear neutrophils(PMN) induced by phorbol myristate acetate(PMA) was investigated with the techniques of ESR，spin trap and oxygen spin probe.The results showed that SPS inhibited the respiratory burst of PMN significantly.10 g/L and 5 g/L SPS almost completely scavenged superoxide anion (O-·2) from the respiratory burst while 10 g/L SPS inhibited the oxygen consumption of PMN markablely， and 1 g/L SPS scavenged 53.2% O-·2.