Abstract: The present study was designed to determine the alteration of plasma lipid peroxidation and erythrocyte Superoxide Dismutase and Glutathione Peroxidase enzyme activities in stored blood. This study is carried out to find out the quantitative alterations and the useful length of stored blood. The whole blood were taken from 10 donors. Red Blood Cells (RBC) were counted in whole blood. The levels of Potassium (P) and lactate dehydrogenate activity (LDH) were measured in plasma for determination of hemolysis. The plasma levels of malondialdehyde (MDA) and erythrocyte Superoxide Dismutase (SOD) and Glutathione Peroxidase (GPx) were studied for determination of lipid peroxidation and antioxidant enzyme activities, respectively. The measurement were performed at the day 0, 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33 and 35 of the storage. The plasma levels of malondialdehyde (MDA) and Potassium and lactate dehydrogenate activity increased (p<0.05) depending on storage time whereas erythrocyte Superoxide Dismutase and Glutathione Peroxidase enzyme activities and Red Blood Cells decreased (p<0.05). The alterations of MDA, SOD, GPx, P, LDH and RBC in the measurement days were as follows: MDA, P and LDH significantly increased at the day 9, 5 and 5 whereas SOD, GPx and RBC decreased at the day 11, 7 and 29, respectively. These results suggest that increased level of MDA and decreased level of SOD and GPx in the stored blood can not improve the vialibilty and longevity of RBC by increasing cell damage caused by free radicals at the days 7-11. To improve the quality of stored blood is to supplement blood donors with antioxidants and vitamins at least one week before blood collection. We conclude that increased level of MDA and decreased SOD and GPx in stored blood which can cause the beginning of hemolysis. It is therefore necessary to control these factors before blood transfusion.