Purpose: To evaluate the characteristic features of mechanical responses and the membrane potential changes induced by repetitive pulsed electromagnetic field (PEMF, 50Hz, 5 mT) in thoracic aorta rings obtained from streptozotocin-induced diabetic and healthy control rats to determine if PEMF could ameliorate problems associated with diabetes. Methods: Sixty male Wistar rats weighing 250-290g were randomly divided into two experimental groups, each containing 30 animals. Streptozotocin was given via tail vein to produce diabetes mellitus (DM) in the first group rats. The second group rats were treated only with % 0.9 saline and considered as non-DM group. Both groups were also divided into two subgroups as DM+PEMF, DM+sham, PEMF and sham, each containing 15 animals. Although the DM+PEMF and PEMF groups were treated, the DM+sham and sham groups were not treated with PEMF. The PEMF treatment occurred four times daily for 30min at 15-min intervals repeated daily for 30 days. Thoracic aorta rings from both DM and non-DM rats exposed to PEMF were evaluated for contraction and relaxation responses and membrane potential changes in the presence or absence of chemical agents that were selected to test various modes of action. Results: Relaxation response of thoracic aorta rings was significantly reduced in DM than non-DM group. PEMF treatment significantly increased the relaxation response of the diabetic rings to acetylcholine, and reduced the concentration response to phenylephrine. Resting membrane potential was significantly higher in DM than in non-DM group. Inhibitors of nitric oxide (NO), both nitro-L-arginine (L-NO-ARG) and L-NO-ARG+indometacin combination, produced a significant transient hyperpolarisation in all groups. Inhibitors of potassium channel activity, charybdotoxin or apamine, produced a membrane depolarisation. However, PEMF did not induce any significant effect on the membrane potential in DM group. Conclusions: Diabetes reduced the relaxation response of thoracic aorta rings. It also affected the membrane potentials of the rings. Treatment with PEMF ameliorated the diabetes-induced impairments in the relaxation response of these rings.