Objective To investigate the diagnostic value of radionuclide imaging in painless thyroiditis．Methods Radionuclide imaging were performed on 20 normal cases, 45 cases with Graves and 30 cases with painless thyroiditis, whose thyroid hormone and 131I-uptake rate test were determined. Results The serum FT3 and FT4 levels in two groups with thyroid disease were al1 significantly increased, whereas the serum TSH level was significantly decreased than those in the control group. The serum FT3 and FT4 level in painless thyroiditis group were lower than those in Graves disease group. Non-visulization of thyroid scintigraphy was observed in painless thyroiditis group. Absorption ratio of 99mTc and 131I in painless thyroiditis group were very low compared with Graves disease group. Thyroid could be well visualized by thyroid scintigraphy in Graves disease group. Conclusion Radioiodine uptake ratio and thyroid scintigraphy may reflect the function and damage scale of the thyroid. It may be an effective method to diagnose painless thyroiditis.