Abstract: OBJECTIVE To investigate relationship between anticoagulation and deactivation ratio on Ⅹ/Ⅱ factor of D-polymannuronicate and estimate the anticoagulation mechanism. METHODS Plasma sample was divided into 6 groups: four D-polymannuronicate groups in different doses, one blank group and one heparin sodium group. APTT, PT and the activity of factor Ⅱ, Ⅹ in each group were determined, then the deactivation ratio on Ⅹ/Ⅱ factor was calculated. RESULTS The anticoagulation as well as the deactivation ratio on Ⅹ/Ⅱ factor was enhanced with the increased concentration of D-polymannuronicate of 50-150 μg·mL^-1. CONCLUSION The possible anticoagulation mechanism of D-polymannuronicate is deactivating the activity of thrombin rather than inhibiting thrombinogen.