Background: Strenuous endurance training compromises the antioxidant defenses of the body and attempts to find supplements to heal gastric ulcers induced by strenuous endurance training are increasing. Objectives: Therefore, the current study aimed at investigating the effects of curcumin supplementation during nine weeks of endurance training on gastric antioxidant capacity (superoxide dismutase; SOD) and lipid peroxidation (malondialdehyde; MDA) of serum in male Wistar rats. Methods: The current applied research was conducted on 26 male Wistar rats aged nine weeks and weighed 215.87 ± 20.49 g. After one week of acclimation to training, the rats were randomly assigned to four groups: the control, curcumin, endurance, and endurance + curcumin. During the nine weeks (five sessions per week), the rats performed an incremental endurance training (up to 70 minutes at 35 m/minute), and the curcumin supplement at 30 mg/kg of body weight was injected intraperitoneally three times per week. SOD activity was assayed by the spectrophotometric method, and serum MDA level was measured utilizing the thiobarbituric acid reactive substances. For data analysis, ANOVA was employed using SPSS version 24. Results: The results of the study revealed that strenuous endurance training significantly reduced the activity of the gastric SOD enzyme (P < 0.05) and increased serum MDA level (P < 0.05), while curcumin supplementation increased gastric SOD enzyme activity, decreased serum MDA level, and resulted in the restoration of antioxidant defenses. Conclusions: Prolonged strenuous endurance training induces oxidative stress to gastric tissue, and curcumin supplementation restores the antioxidant defense of the gastric tissue and body.