Introduction: Electrocardiogram (ECG) indices are valuable tools for the diagnosis, depolarization, and repolarization of the myocardium during aerobic Exercise and detraining. The purpose of this study was to investigate the effects of 12-week Moderate-intensity aerobic Exercise and 5 months detraining on ECG indices in post-menopausal women. Methods: Twenty-four post-menopausal women aged 50-70 years were randomly assigned to Exercise (E, n = 12) and control (C, n = 12) groups. E group performed 12-week moderateintensity aerobic Exercise program (W-WJMIAEP-R), and then 5 months detraining remained, but the C group participated in no intervention during the 8 months of the study. The ECG indices were measured at baseline, after 12-week Exercise, and after 5-month detraining. Results: After 12 weeks, ECG indices were not significantly different (P > 0. 05) between the groups, except for P-R Interval (P ≤ 0. 05) which was significantly higher in the E group. After 5-month detraining, indices were not significantly different between the groups (P > 0. 05), except for P-R segment and S-T Interval (P ≤ 0. 05) which were significantly decreased in the E group. Conclusion: The results suggested that 12 weeks of walking & jogging aerobic Exercise with 65-70% maximal heart rate increased the P-R Interval. In addition, P-R segment and S-T Interval decreased after 5 months of detraining period in sedentary post-menopausal women.