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Introduction: Considering the increasing incidence of atherosclerosis and cardiovascular disorders in diabetes mellitus, this study was conducted to evaluate the beneficial effect of two-month administration of Plantago Psyllium (PP) seed on the contractile reactivity of isolated aorta in diabetic rats. Materials and Methods: In this experimental study, 32 male Wistar rats were randomly divided into four control, PP-treated control, diabetic and PP-treated diabetic groups. To induce diabetes, Streptozotcin (STZ) was intraperitoneally administered (60mg/Kg). PP-treated groups received PP mixed with standard pelleted food at a weight ratio of 6.25%. After 2 months, contractile reactivity of thoracic aortic rings to KCl and Noreadrenaline were determined using isolated tissue setup. Data was analyzed using ANOVA and Tukey tests. Results: Serum glucose level showed a significant increase in diabetic group after one and two months (p<0.001), but it,s decrease in PP-treated diabetic group was not significant in comparison to diabetic group. Also PP-treated diabetic group showed a lower contraction to KCl (p<0.05) and noreadrenaline (p<0.01) as compared to diabetic group. Meanwhile, there was no significant difference between control and PP-treated control groups regarding contractile reactivity. Conclusion: It can be concluded that oral administration of PP for 2 months can decrease the contractile responsiveness of vascular system and this may prevent the development of hypertension in diabetic rats.