Two sulfated chitosan derivatives were prepared in this paper (CSA and CSB that is low and high replacement) and their medical effect was researched. Aim: to study the effect of chitosan derivatives on thrombus formation and cruor time in mice. Method: sixty mice were divided in to six groups and each group was raised with chitosan derivatives (CSA、CSB) 200 and 600mg /kg, aspirin 10 mg /kg, and 0.5% sodium carboxymethyl cellulose 2 ml /mice respectively. The levels of thrombus formation and cruor time were calculated in mice. Conclusion: two kinds of sulfated chitosan of the different sulfur con tent had been successfully prepared, that is CSA:DD 21.23%;CSB:DD 42.21%.Their yields are all over 90%;CSA、CSB at doses of 200mg /kg barely in fluence the rate of thrombus formation and cruor time, however, CSB at doses of 600 mg /kg significantly decreased the weight of thrombus and increased cruor time in mice: decreasing 14.21% thrombus weight and increasing 14.31% cruor time.