Objective: Suppressive therapy with levothyroxine is the main step in treatment of differentiated thyroid cancer. Recent studies have suggested that metformin may have a suppressive effect on TSH level. Methods: We performed a cross-sectional analysis among 30 subjects with type 2 diabetes underwent total thyroidectomy due to differentiated thyroid cancer during five years and were receiving levothyroxine suppression therapy. Patients were divided into two groups depending on metformin use: the non-metformin group included 10 patients; the Metforim group 20 patient. TSH and thyroid hormone values were measured after 3months after treatment. Results: The mean age, weight, BMI and TSH level were not significantly different between the metformin and the non-metformin. However, Levothyroxine dosage was significantly differences between the metformin and the non-metformin groups: 172.2 μg in the non-metformin group versus 162.5 μg in the MF group (P = 0.5). Conclusion: Patients receiving metformin treatment need a lower thyroxine dose than patients who do not receive the drug of the patients with diabetes mellitus type 2.