Objective: The aim of this study was to evaluate the effect of radioactive iodine (RAI) ablation therapy on the complete blood count (CBC) in thyroid cancer patients. Materials and Methods: One hundred sixty four patients undergoing RAI ablation therapy after total thyroidectomy were included. CBC results were available from the patients’ medical records at the time of ablation and at the 1st, 6th, and 12th months after RAI therapy.Results: Hemoglobin (Hb), white blood cell (WBC) and platelet (Plt) values were significantly lower than baseline at 1 month after treatment (p