Oxidative stress is the major mechanism impairing cell homeostasis, inducing cell death and tissue damage in sulfur mustard (SM)-exposed individuals. The aim of the present study was to evaluate time course changes of oxidative stress in the mice exposed with 2‑chloroethyl ethyl sulfide (CEES) as SM analog. For this purpose, male BALB/c mice were divided into control groups and experimental groups that received CEES (10 mg/kg) through intraperitoneal injection. In both groups, animals were euthanized at three periods: short (12, 24 h and 1 week), medium (1, 2 and 3 months) and long-term (5 and 6 months) after CEES exposure. Oxidative stress indices and the antioxidant defense systems were evaluated in lung and liver tissues. The time course findings in both tissues showed a significant increase in oxidative damage markers such as malondialdehyde (lung P < 0.001, liver P < 0.001), protein carbonyl (lung P < 0.0001), and 8-hydroxy-deoxyguanosine (lung P < 0.0001, Liver P < 0.0001) and also a significant reduction in the antioxidant defense system including reduced glutathione level (lung P < 0.001, Liver P < 0.001,), activities of catalase (lung P < 0.01 and liver P < 0.05), superoxide dismutase (lung P < 0.05), glutathione S‑transferase (lung P < 0.05, liver P < 0.01), glutathione peroxidase (lung, P < 0.05, Liver P < 0.05) and glutathione reductase (lung P < 0.001, liver P < 0.01) in the long-term. However, these changes occur with less intensity in the short-term and return to the normal status in the medium-term. Moreover, there was a positive time course correlation between oxidative damage indices and the percent of histopathological damage in both tissues (P < 0.05). This correlation finding confirms and supports the fact that time course oxidative-antioxidant imbalance plays an important role in the development of SM-induced acute and delayed injuries.