Background & Aims: Cardiovascular diseases are one of the most important complications of diabetes mellitus and hyperglycemia induced oxidative stress can increase hyperglycemia and the risk of diabetes complications. So the aim of the current study was to examine comparison of the effect of 6 weeks aerobic training on the activity of catalase enzyme and malondialdehyde in heart tissue of healthy and streptozotocin-diabetic male Wistar rats. Materials & Methods: In this experimental study, 24 adult male rats with 10 weeks of age were assigned to 4 groups of 6: diabetic training group (DT), diabetic control group (DC), healthy training group (HT) and healthy control group (HC). The exercise program included 6 weeks of incremental moderate intensity aerobic training. 24 hours after the last training session the heart tissues for catalase and malondialdehyde activity measuring by spectrophotometric and wavelength measurement methods, respectively were extracted. For comparison, one-way ANOVA test and scheffe post-hoc test with a statistical level of (P≤ 0. 05) were used. The required information was then processed and analyzed by SPSS version 23 software. Results: After 6 weeks of aerobic training, level of catalase enzyme increased significantly in healthy training group and diabetic training group compared to healthy control group diabetic control group, respectively (P≤ 0. 05). Malondialdehyde levels significancy decreased in healthy training group compare to diabetic control group (P≥ 0. 05). But there was no significance difference between diabetic training group and diabetic control group, although a little increase observed in diabetic training group but it was not significant (P≤ 0. 05). Conclusion: Based on the results, it seems that moderate intensity aerobic exercise is likely to have a favorable effect on the antioxidant system of the heart tissue of diabetic rats.