Human Adenosine deaminase is an essential enzyme for modulating the bioactivity of thyroid hormones, and It is important for the maturation and differentiation of lymphocytes, although its clinical importance in thyroid diseases have yet to be identified. Objective: The aim of the current study is to determine the Adenosine deaminase concentration in healthy controls, and in autoimmune thyroid diseases such as Graves' Disease, and Hashimoto's Thyroiditis. Patients and methods: A total of 183 serum specimens of 103 female patients with autoimmune thyroid diseases and 80 healthy control groups were included in this study and collected from the Baghdad Medical City, Iraq. Quantitative Human Adenosine Deaminase ELISA kits were used to estimate concentration of serum Adenosine deaminase. Results: There were a highly significant differences between thyroid patients and controls regarding TSH, T4 and adenosine deamainase serum levels (P-value 0.000), while no significant differences were seen with T3. On the other hands, There was a significant difference in adenosine deaminase protein level of autoimmune thyroid diseases patients in compared with controls (8.39±4.74 vs. 6.99±2.411, P<0.05). The results also indicate that both of age and BMI shows significant differences in patients compared with controls (42.63±12.97 vs. 38.94±12.82, P<0.05). Conclusion: There were a highly significant differences between thyroid patients and controls in TSH, T4, Anti-TPO and anti-TG, except T3.