Objective To investigate the relationship between the changes of thyroid 131I uptake ratio in subacute thyroiditis and clinical examination. And try to establish a standard to distinguish the low-level 131 Iuptake ratio caused by subacute thyroiditis and by cystic goiter (or cystadenoma) rupture. Methods The data of thyroid 131I uptake ratio of 44 cases got according to the clinical nuclear medicine examination standard was reviewed and analyzed. Results 1. The 131I uptake ratio in 36 subacute thyroiditis patients were lower than the normal level (P<0.001), including 26 peak ahead cases (2h 3.37±2.53%, 4h 4.54±1.12%, 24h 2.44±1.18% ) . 2. The 131I uptake ratio in 8 cystadenoma rupture patients decreased apparently, too. But no peak ahead case appeared. Conclusions The subacute thyroiditis is characterized not only with the apparent decrease of 131 I uptake ratio, but also with peak ahead (72.22%) .