Introducton/Background: Thyroid disorder are commonly associated with Type 2 Diabetes mellitus (T2DM). Since HbA1c is the screening test for Diabetes, so this study was done to find out any co–relation between thyroid disorder and HbA1c and predict the value of it to diagnose a person as diabetic in the back ground of thyroid disorder. Objective: To find out any co–relation between thyroid dysfunction and the value of HbA1C and to predict a co–relation of range of abnormality in diabetic patients. Material and Method: This observational prospective study was conducted on 130 newly diagnosed diabetic patient’s of age between 18years to 88years presenting to the OPD and IPD of Rohilkhand Medical College and Hospital Bareilly between November 2015 to October 2016. All patients of both genders underwent investigation of thyroid profile, blood glucose (F&PP) and HbA1C , screening after through clinical history and examination was done. Data was collected, computed and analyzed statistically. Results: More than half of the patients ( 62.2%) with normal thyroid condition (euthyroidism) had HbA1c>8 while 40% patients with hyperthyroidism and 45.5% patients with hypothyroidism had HbA1c >8. Chi square test was applied to check the statistical relation of thyroid abnormality in diabetic patients with level of HbA1c. There was statistically significant relationship (p <0.05). Conclusion: A significant number of diabetics (37.8% ) had thyroid dysfunction. The prevalence of hypothyroidism was more than hyperthyroidism. The value of HbA1c should be interpreted differently in patients having thyroid disorder in newly diagnosed diabetics in comparison with patients having no thyroid disorder. In this study it was found that patients having thyroid dysfunction in diabetes had higher HbA1c ( >8) as comparing with the patients having same range of blood glucose without thyroid abnormality.