The aim of this study was to investigate the effects of 12 min run test on oxidative stress, some antioxidant enzyme activities, and muscle and DNA damage. Twenty two healthy and well trained male athletes were recruited to this study. The 12 min run test, cooper test, was applied to the participating athletes. The blood samples were taken before, immediately after and 24 h after the run test, and sera and plasma were separated and then stored at -80 degrees C until the analysis. Serum MDA and NO levels as the indicators of oxidative damage; serum SOD and CAT, plasma GPx activities as the indicators of antioxidant defense system; serum 8-OHdG as the indicator of DNA damage, CK and LHD enzyme activities as the indicators of muscle damage, and glucose level were measured. Serum SOD, NO, CAT, and 8-OHdG levels showed no significant changes before, immediately after and 24 h after the run rest. There was a significant decrease in serum MDA level immediately after exercise, which is returned to baseline level after 24 h-rest period (p<0.05). Serum LHD (p<0.001) and CK activities (p<0.05) and glucose level (p<0.001) increased immediately after exercise but these increments returned to pre-exercise level after 24 h-rest period. Acute twelve minute endurance exercise increased CK, LDH and glucose decreased oxidative stress and whereas has no effect on antioxidant capacity and DNA damage in trained young men.