Background: Chemical gas, especially sulfate mustard (SM) was used against Iranian forces repeatedly during the Iraq war. Gas effects on various tissues within the body depend on amount and duration of exposure. According to the prevalence of oral lesions, this study was conducted in Zahedan city on the chemical warfare. Material and Methods: This descriptive cross-sectional study was performed on 70 patients. After obtaining the patient's consent form, a demographic questionnaire was completed by patients and the patients were examined. If there was soft tissue lesions, the cases were examined more closely. All data were collected on special forms and statistical analysis was performed by the SPSS computer program. Results: Among the 82 patients, 52 patients were with oral lesions and 18 patients were with healthy oral mucosa. The most common oral lesions seen in the study were pigmentation (52.8 %), ulcer (42.8%) and bleeding and gingival enlargement (34.2 %) and white lesions [picking (28.5 %) and Peel off (22.8 %)], respectively. Conclusion: The most common lesion sites were in the gums and tongue. Many patients referring were not informed of the lesions in their mouth and this problem emphasizes that the periodic oral examinations are required by specialists.