Obesity influences semen quality by hormonal imbalance. Therefore, the aim of this study was to examine the effect of moderate and intensive aerobic training on obese male rats' reproductive function. 30 obese male rats were assigned to moderate training (n=10), intensive training (n=10) and control (n=10) groups. A matched control group of normal weight rats (n=10) were also recruited for baseline comparison. The moderate (60 min/day swimming, 3 days/week) and intensive (150 min/day swimming, 5 days/week) training program were performed for 8 weeks. After the 8 weeks, rats were anesthetized and hormonal and seminological profiles were evaluated. At the baseline, normal weight rats had significantly higher spermatogenesis quality (P<0.03) and testosterone level (P<0.02) than obese rats. After the moderate aerobic training, body weight (P<0.001) and spermatogenesis quality (P<0.04) significantly improved. In contrast, spermatogenesis quality (P<0.03) and testosterone level (P<0.03) significantly decreased after the intensive aerobic program. The present findings suggested that moderate swimming training may lead to improvement in spermatogenesis quality in obese rats while intensive training has a negative effect on spermatogenesis quality.