Context: Sulfur mustard (SM) as a cytotoxic and blistering agent can alkylate a variety of cellular components, causing the incidence of ongoing oxidative stress. Objective: The present study was conducted to assess oxidative stress index (OSI) in SM-exposed veterans with long-term pulmonary complications. Methods: Participants consisted of 289 SM-exposed individuals with pulmonary complications (classified into three groups: mild, moderate and severe) and 66 healthy individuals as the control group. Enzymatic and non-enzymatic antioxidant and also trace elements were measured in the study groups. Moreover, some of oxidative stress indicators consist of malondialdehyde (MDA), protein carbonyl (CO), total antioxidant (TA) and total peroxide (TPX) were measured and then OSI was calculated. Results: Glutathione-S-transferase (GST) activity and vitamin C (Vit C) were significantly decreased in SM-exposed patients as compared with controls. Besides, Cu level and Cu/Zn ratio in SM-exposed veterans showed a significant correlation with the severity of the diseases. Serum TPX was significantly increased in SM-exposed individuals, as a result of which the OSI was slightly higher in them than controls. This can be considered as an indicative for oxidative stress in SM-exposed patients. Conclusion: This study suggests a particular role for TPX, Cu, Vit C and GST in SM-induced pulmonary complications. Therefore, a special attention should be paid to these factors in designing therapeutic protocols, which can reduce the progression risk of the disease.