Diabetes is a multisystem disease that can produce both microvascular and macrovascular problems. The presence of significant microvascular circulation and connective tissue in the lungs indicates that the lungs might be a "target organ" in diabetic patients. Diabetes is not directly linked to any specific pulmonary pathology, hence diabetic patients don't get routinely screened for lung disease. However, this depends on duration of diabetes and glycaemic control. Patients can develop multi organ manifestations secondary to micro/macrovascular complications, which inturn affects the connective tissue and circulation of lung leading to multiple pulmonary disorders. The study's goal was to investigate pulmonary function in patients with diabetes mellitus using spirometry, as well as the correlation between pulmonary function with disease duration and Hba1c level.The hospital-based cross-sectional observational study was undertaken from August 2022 to December 2023. Total of 140 diabetes patients were recruited. All patients were subjected to PFT by spirometry after complete clinical history with particular emphasis, physical examination, imaging by chest X ray to rule out pre-existing lung diseases and HbA1c. In this study, out of 140 diabetics 83 were male and 57 were female with the mean age of 55.63 years. The results of the present study showed 66.3% abnormal PFT with 39.2% restriction (mean FVC-75.12), 12.1% obstruction (mean FEV1-68.066), 15% mixed pattern. Negative correlation was found with duration of diabetes and PFT which is statistically significant. This study shows significant abnormality of PFT with restrictive pattern as predominant followed by mixed and obstructive patterns. In this study significant reduction in pulmonary function has been noted with duration of diabetes and HbA1c. There is a negative correlation between pulmonary function with duration of diabetes and HbA1C.Hence this study shows that as duration of diabetes increases, lung function decreases.