OBJECTIVE: To evaluate the protective effect of Zataria multiflora extract, an antioxidative medicinal plant, against cyclophosphamide (CP)-induced oxidative lung damage in mice. METHODS: Mice were intraperitoneally pre-treated with various doses of Zataria multiflora extract (50, 100, 200, and 400 mg/kg) once daily for 7 consecutive days. Animals were then injected with a single 200 mg/kg intraperitoneal dose of CP 1 h after the last administration of O. vulgare. Twenty-four hours later, mice were euthanized, the lungs were immediately removed, and biochemical and histological studies were conducted. RESULTS: A single dose of CP markedly altered the levels of several biomarkers associated with oxidative stress in lung homogenates. Pretreatment with Zataria multiflora significantly inhibited the elevation of lipid peroxidation level and the depletion in glutathione content, and superoxide dismutase and catalase activities induced by CP in lung. In addition, Zataria multiflora effectively alleviated CP-induced histopathological abnormality and pulmonary damages in mice lung tissues. CONCLUSIONS The results reveal that Zataria multiflora protects lung tissues from CP-induced toxicity and suggest a role for oxidative stress in the pathogenesis of lung toxicity produced by CP in mice. Because Zataria multiflora has been extensively used as an additive agent and is regarded as safe, it may be used concomitantly as a good supplement for reducing organ toxicity in patients undergoing chemotherapy, besides their consolidated ethnopharmacological uses.