In patients with beta -thalassemia major, the most important cause of mortality and morbidity is organ failure due to deposits of iron.. In this study, the nature of the kidney injury and possible pathogenetic factors were investigated. Seventy children with beta -thalassemia major and 14 age and sex-matched healthy children were involved in the study. Blood and timed urine samples were obtained for hematological and biochemical tests. The mean values of blood urea nitrogen (BUN), serum creatinine, creatinine clearance, serum sodium, urine osmolality, fractional excretion of sodium, potassium, and uric acid were not statistically different between the groups. Serum levels of potassium, phosphorus, and uric acid and the urine volume, high urinary protein to creatinine (U-P/Cr), urinary N-acetyl-beta -D-glucosaminidase to creatinine (U-NAG/Cr), and urinary malondialdehyde to creatinine, (U-MDA/Cr), and the tubular phosphate reabsorption (TRP) values were statistically different between two groups (P<0.05). Increased serum levels of potassium, phosphorus, and uric acid in the patient group were attributed to the rapid erythrocyte turnover. The presence of high U-P/Cr, U-NAG/Cr and U-MDA/Cr, ratios shows that in these patients with proximal renal tubular damage may be secondary to oxidative lipid peroxidation mediated by the iron overload.