BACKGROUND: Polysaccharide sulfate has bean hot focus in recent research.Regarding anticoagulant property of sulfated polysaccharides, recent studies mainly explored degree Of substitution, and there are rare studies concerning relative molecular mass and spatial structure.OBJECTIVE: To study the anticoagulant activity of the sulfated agarose with different relative molecular masses.METHODS: With formamide as dispersing agent,agarose was sulfated with the method of chlor0sulfonic acid-pyridine.The product was graded and purified with dialysis bag.Two kinds of sulfated agarose with different molecular masses were obtained,and their anticoagulant properties were checked by assays of the activated partial thromboplastin time,thrombin time.RESULTS AND CONCLUSION:.Two kinds of sulfated agarose had similar degree of substitution and sulfation position,whereas their molecular weight was different.The bioassay results of coagulation index demonstrated that the anticoagulant activity of agarose improved with the increasing of molecular mass within a certain range.Relative molecular mass had an important effect on the anticoagulant activity of the sulfated agarose.