Male rats were equally divided into trained rest (TR), trained exhaustive exercise (TE), untrained rest (UR), and untrained exhaustive exercise (UE). Endurance training consisted of treadmill running for 1.5 h/d, 5 days a week for 8 weeks reaching the speed of 2.1 km/h at the fortieth week. For acute exhaustive exercise, graded treadmill running was conducted reaching the speed of 2.1 km/h at 95th min, 10% uphill, continued until exhaustion. Testicular tissue malondialdehyde (MDA), antioxidant potential (AOP) levels, superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), glutathione-S-transferase (GST), glutathione reductase (GR) and catalase (CAT) activities were determined. There was a slight decrease, but not significant, in the SOD activity in UE group compared to TE and TR groups. Activity of GSH-Px decreased in the UE group compared to UR, TR and TE groups. Acute exhaustive exercise did not affect testicular tissue GSH-Px activity in trained rats. Testicular tissue GST activity of the UE group was similar to TE group, but lower than UR and TR groups. In UE group, testicular tissue AOP values were lower than UR, TR and TE groups. The oxidative effects of acute exhaustive exercise on the rat testis decreased with endurance training. Endurance training prevents oxidative injuries by eliminating oxygen radicals and inhibiting lipid peroxidation via preventing decreases in antioxidant enzyme activities.