Renal anemia improves after treatment of erythropoietin (EPO) but its mechanism is not clear. To evaluate the effect of erythropoietin on red blood cell survival (RBCS) and oxidant system which is important in renal anemia, 22 dialysis patients (17 hemodialysis, 5 continue ambulatory peritoneal dialysis) with mean age 41.7±14 yrs. and 44 healthy subjects with mean age 44.8±9 yrs. were studied. 50 Ib'/kg EPO was giventwo day/weekly S.C. to patients and continued with 61 ±21 IU/kg for 16 months. In patients group, decreased hemoglobin, heamatocrite and erythrocytes values at initial were significantly increased at the end of four months than continued the elevation by 16 months. Serum albumin and transferrin values that lower at initial, increased after four months than continued further 12 months. Vitamin E, intraerythrocytes superoxide dismutase, plasma free carnitine increased and malonyldealdehyd decreased at the end of 16 months. Initial red blood cell survival (using Cr-51), was significantly lower than controls (18.4±6.7 vs. 29.4+7.2 d). It prolonged significantly after in both 6 (25.5±7.3 d) and 12 months (29.4±6.7 d). We observed that EPO treatment prolongs RBCS by decreasing lipid peroxidation and increasing antioxidants in dialysis patients.