Aim: Correlation between Adenosine Deaminase activity and Insulin level in patients with Type 2 Diabetes Mellitus. Material & Method: We measured the serum level of Adenosine Deaminase (ADA), Insulin and Fasting Plasma Glucose (FPG) in 50 patients with type 2 diabetes and 50 healthy controls. Subjects included in study were known diabetics for 5 years or more. Results: The levels of Serum Adenosine Deaminase and Insulin were highly significant (p<0.001) in study group in comparison to control group. Adenosine Deaminase was positively correlated with Fasting Plasma Glucose (r=0.6146, p<0.001) and Insulin (r=0.3022, p<0.05) in diabetic patients. Insulin was positively correlated with Fasting Plasma Glucose (r=0.4728, p<0.001) in diabetic patients. Conclusion: Present study concludes that serum Adenosine Deaminase activity and Insulin levels significantly increased in type 2 diabetes mellitus. Both Adenosine Deaminase and Insulin positively correlated with each other and also with Fasting Plasma Glucose. As adenosine deaminase can serve as an immunological marker and has a probable role in oxidative stress along with its effect on insulin actions by decreasing levels of adenosine, Adenosine Deaminase can be a useful parameter in the pathophysiology of type 2 diabetes mellitus.