Background: The respiratory diseases are major cause of disability and mortality, worldwide. Among the significant airborne pollutants affecting lung health, tobacco smoke stands out. Its detrimental effects include the promotion of inflammation, apoptosis, and oxidative stress in patients with chronic obstructive pulmonary disease (COPD) and lung cancer. Oxidative stress has widely contributed to diverse diseases, including COPD, and lung cancer. So there is an evidence suggested that excessive nitric oxide (NO) in lung tissue plays an important role in activation of platelet, stimulate chronic inflammation, and oxidative stress that leads to destruction of lung capillary endothelium and microangiopathy. The objective of this study was to examine the significant involvement of nitric oxide as a marker of oxidative stress related to inflammation and apoptosis in COPD and lung cancer patients. Methods; the levels of nitric oxide were measured using the ELISA method in serum samples from healthy controls (n=10), COPD patients (n=16), and lung cancer patients (n=16). Results: The results demonstrated a significant increase in nitric oxide levels in both the COPD and lung cancer groups compared to the healthy control group. Conclusion: In conclusion, these findings collectively suggest that elevated levels of nitric oxide are associated with oxidative stress in COPD and lung cancer patients and play a crucial role in the damage to lung epithelial cells and the development of both COPD and lung cancer