The objective of this study is to determine the prevalence of thyroid dysfunction in Major Depressive Disorder and the factors that were associated with the severity of MDD. Methods: A total of 140 major depressive disorder patients researched are subjected for blood sampling to determine the blood thyroid abnormalities. The severity of illness of MDD was determined by the duration of illness, frequency of admission/ suicidal attempts, and the Hamilton rating scale for depression (HAM-D). Results: Thirty-one of the 140 patients had thyroid dysfunction. There was no significant difference in the severity of illness among patients with MDD between thyroid dysfunction and normal function group (p=0.024). Conclusion: Patients with MDD had high prevalence of thyroid dysfunction; however, the former had no correlation with later. ASEAN Journal of Psychiatry, Vol. 18 (1): January – June 2017: XX XX.