Background: Type 2 Diabetes mellitus is a metabolic syndrome that leads to hyperglycemia and complications in many organ systems. There are many ways to control hyperglycemia including diet, exercise, drugs, and insulin. Aim of the study: The purpose of this study was to determine the effects of diaphragmatic breathing exercises on blood sugar levels and to identify the effects of regular diaphragmatic breathing exercise on HbA1c. Subjects and Methods: The study design used was a randomized controlled trial. Random sampling technique was used. Data was collected from working female nurses of Services Hospital Lahore and Jinnah Hospital Lahore who had type-2 diabetes mellitus. By using Ballot method 64 subjects were selected and equally divided into 2 groups randomly (32 subjects were in an interventional group and 32 in the control group). Data were analyzed using SPSS version 20. Mean difference was measured by using independent sample t-test and paired t-test to see the pre and post effects of the same group. Results were summarized as mean and standard deviation. Results: The study results indicated that there was a significant reduction in fasting blood sugar level (p=0.009), post prandial blood sugar level (p=0.002) and post interventional blood sugar level (p=0.000) in the 9th week of the activity (breathing exercise). Pre and post the interventional mean difference in fasting blood sugar level was highly significant in the 12th week of intervention (p=0.000). No significant difference was found in the results of HbA1c (p=0.963). Conclusion: Diaphragmatic breathing exercise has favorable effects in controlling blood sugar levels among diabetes type-2 patients if it is combined with other exercises or therapies. Only breathing component cannot maintain the normal blood sugar level.