Background: Ionizing radiation affects human health as it breaks the chemical bonds of the molecules and damages DNA through the manufacturing of free radicals, resulting in apoptosis of proliferative cells/ damage to erythrocytes which may influence the quality of RBC concentrates. Objective: Our aim was to evaluate the effect of occupational exposure to low dose ionizing radiation versus high dose exposure during radiotherapy on met Hb level. Subjects and Methods: 150 individuals were included divided into two groups; group I, includes 50 radiation workers (RWs) compared to 25 healthy volunteers' as control group for radiation workers who never exposed to radiation in their work. Group II includes 50 breast cancer patients who were treated with post-operative radiotherapy compared to 25 matched age and sex healthy female volunteers' as control group who had never worked in radiation-related jobs. Methemoglobin was assayed by ELISA. Serum ferritin and iron by automated quantitative enzyme linked fluorescent assay. Results: A significant decrease in WBCs, MCV and serum ferritin was observed among RWs in comparison to control group. Methemoglobin levels and Reticulocyte % were significantly higher in RWs in comparison to BCPs after radiotherapy. Mean values of WBCs, HB and RBCs were significantly lower in BCPs after radiation therapy when compared to radiation workers while there was insignificant difference in mean values of Ht, MCV, MCH and RDW. Conclusion: Serum methemoglobin levels and Reticulocyte % can be used as biological dosimeters for early assessment of the absorbed dose in radiation workers.