Abstract: The effect of anti- aging and structure- function relationship of fucoidan from kelp was studied. The fucoidan was extracted from kelp and FSP- 1,FSP- 2,FSP- 3 were purified. Elemental analysis,gel permeation chromatography coupled with multi- angle laser light scattering( GPC- MALLS) and GC analysis were applied to investigate the three components. In order to study the effect of anti- aging of three components from kelp,administered medicine was given to rats with subacute senile model by D- galactose,then some indexes were determined. Compared treatment group with senile model group,indexes of thymus and spleen( p < 0.01) were promoted by FSP-2 and FSP- 3,moreover,the effect of FSP- 3 was more significant than FSP- 2. The activity of superoxide dismutase( SOD) and GSH- PX in blood were significantly promoted,but the content of malondialdehyde( MDA) was decreased by three components from kelp. Three components from kelp had the activity of anti- aging,and the activity of anti- aging was in relation with the content of sulfate groups,molecular mass and sugar composition of them.