The results of trials regarding the effect of cobalt on the reperfusion injury are controversial. In this study, we investigated whether cobalt had a role on the prevention of reperfusion injury in the kidney of wistar rats. Rats were divided into seven groups, each consisting of 10 rats. Laparatomy and nephrectomy was only performed in group 1. In groups 2, 4 and 5 for 45 minutes and in groups 3,6 and 7 for 60 minutes ischemia were induced by temporary clamping of the bilateral renal pedicles. Additionally, intravenous cobalt nitrite had been administered 5 mg per kg in groups 4 and 6; 10 mg per kg in groups 5 and 7 during the ischemic period. After ischemic period reperfusion for 60 minutes were carried out in all groups. At the end of the study, blood samples were collected for measuring serum cobalt levels and erythrocyte glutathion peroxidase activity from all rats and after that bilateral nephrectomy was performed, all rats were sacrified. In the cortex and medulla of kidney as an indicator of severity of reperfusion injury Malone dialdehyde levels were examined respectively. The Statistical analyses was performed with Kruskal Wallis test and Mann Whitney -U test . While medulla MDA levels of groups 2-3 were found higher than control group (group 1), cortex MDA levels remained same. In cobalt nitrite administered groups (group 4,5,6 and 7) cortex MDA levels were determined higher than group 1,2,3 whereas medulla MDA levels didn't change. Erythrocyte gluthation peroxidase activity increased significantly in cobalt groups (4,5,6 and 7) (p<0.05). We conclude that reperfusion injury is not prevented in the kidney, moreover may be increased cortex MDA tissue levels by cobalt.