Abstract: Objective: To study the effect of CM- chitosan with different molecular weight on blood glucose in diabetic mice.Methods: The diabetic model was established by intraperitoneal injection of 160 mg / kg STZ( Streptozocin),and the mice were randomly divided into model group,positive control group,experimental group( high molecular weight CM- chitosan group,middle molecular weight CM- chitosan group,low molecular weight CM- chitosan group),and blank control group,with 12 rats in each group. Experimental group were daily given experimental drugs according to 990 mg / kg.b.w,model group and blank control group were daily given the same volume of distilled water,the positive control group were daily given acarbose tablets according to 20 mg / kg.b.w,totally for28 days. After the last time,the fasting blood glucose and the glucose tolerance were measured. Results: The different molecular weight of CM- chitosan had no significant effect on the body weight of mice( p > 0.05).Compared with the model group,the low molecular weight group could significantly reduce the blood glucose concentration( p < 0.01),and the molecular weight can reduce the blood glucose concentration( p < 0.05),but no significant effect of high molecular weight group,and the glucose tolerance of diabetic mice were improved in all the experimental group. In summary,the effect of low molecular weight CM- chitosan was the best,the middle molecular weight CM- chitosan was the second,the high molecular weight CM- chitosan was the last.