The leading cause of gastritis and its complications is Helicobacter pylori Radioactive iodine ( 131 I) accumulates significantly in the stomach after consumption. On this basis, we decided to determine whether different doses of 131 I in the stomach would be effective in eradicating the infection. Methods: All patients with hyperthyroidism or differentiated thyroid carcinoma who were referred for 131 I treatment were invited to the study. A stool antigen test was conducted before consumption of 131 I (0.15-5.5 GBq) and was repeated 2 mo later to detect H. pylori infection. Results: H. pylori positivity was found in 51.8% (14/27) of the patients. At 2 mo after treatment, 13 of the 14 patients with differentiated thyroid carcinoma or hyperthyroidism who had been identified as positive for H. pylori stool antigen before 131 I administration were still positive, representing a nonsignificant eradication rate of 7.1%. Conclusion: Administration of 131 I to patients with H. pylori did not show potential to eliminate the infection.