Objective: Sulfur mustard (SM) has been known as an effective chemical agent and was used in 1980s during Iran-Iraq war against Iranians. At the present time there are more than 40.000 people suffering from pulmonary lesions due to mustard gas in Iran. Though much is known about the gross pathology of SM damage, the molecular and cellular basis for this pathology is not well cleared. One of the most important proteins which are involved in inflammatory responses is Nuclear Factor kappaB protein family .It belongs to members of DNA-binding protein factors which is necessary for transcription of many proinflammatory molecules. In our research, we examined the role of NF-kappaB1/RelA in pathophisiology of lung. Materials and Methods: We investigated 10 normal individuals and 20 SM induced patients. Expression of NF-κB1/RelA in control and the SM exposed samples was measured by Real-time PCR and localization of NF-kB1 protein was detected by immunohistochemistry staining. Results: Our result revealed that expression levels of NF-κB1 and RelA were upregulated 0.64- 6.50 folds and 0.83-8.34 folds respectively in the SM exposed patients in comparison with control samples. Conclusion: As we know this is the first finding of induction of NF-κB in patients exposed to SM. NF-κB1/RelA May plays a major role in inflammation induced by mustard gas or even cell survival in bronchial wall of patients.