Background: This study aimed to assess several biochemical and oxidative stress parameters before and after radioiodine therapy in patients with well-differentiated thyroid cancer who consumed a low iodine diet and withdrawal of levothyroxine after total thyroidectomy.Methods: We enrolled 40 candidates for radioiodine therapy. Blood sampling was performed prior to as well as 72 h after consumption of 125-200 mCi of 131I. Total protein, aspartate aminotransferase, alanine aminotransferase, alkaline phosphatase, and creatinine were measured. Oxidative stress parameters that included malondialdehyde and protein carbonyl levels were also assessed.Results: There were significantly decreased total protein, creatinine, aspartate aminotransferase, and alanine aminotransferase levels (P<0.001) after treatment. However, malondialdehyde levels increased significantly (P<0.05) over the studied time.Conclusion: We found that radioactive iodine absorption in peripheral tissues due to a low-iodine diet and levothyroxine withdrawal could relieve iodine deficiency in the liver and kidneys which resulted in reduced total protein, aspartate aminotransferase, alanine aminotransferase, and creatinine levels. However, it induced oxidative stress by increasing malondialdehyde levels in the blood.