Objective: The radionuclide imaging of thyroid plays an important role in the diagnosis and treatment of thyroid disease.One research showed that high dose iodine depressed the thyroid 99mTcO4.uptake.The aim of this study was to study the effect of different levels of iodine on thyroid 99mTcO4-uptake.Methods: 288 Kunming mice were divided into 8 groups at complete random.One was control group fed with tap water, the others were high iodine groups fed with water containing KIO3 at 50,100, 150, 200, 250, 500, 5000μg/L, respectively.When the mice were fed for 7 days, the thyroid weight and thyroid uptake of 99mTcO4-were measured at different time points.Results: When iodine dose was 150ug/L or greater, the thyroid of mice showed decreased 99mTcO4-uptake.Conclusions: In this study, we observed that the thyroid uptake of 99mTcO4-decreased as the iodine dose increased.The thyroid uptake of 99mTcO4-in the group with 150μg/L or higher KIO3 was significantly different from that of the control group at various time points.