Abstract: Objective （ ） To evaluate the internal exposure levels and risk in nuclear medicine workers NMWs engaged in Methods radionuclide therapy in Guangdong Province. A total of 61 NMWs from eight hospitals in Guangdong Province were selected as the study subjects using the convenient sampling method. The 0.364 MeV full energy peak efficiency was detected in （ ） in vitro ， - deltoid muscle of right upper arm as background and thyroid gland by direct measurement method and the iodine 131 （131 ） Results ，131 I activity in thyroid gland was calculated to evaluate the internal irradiation level. Among the 61 NMWs I was ， detected in the thyroid gland of four nuclear medical staffs in three hospitals and the detection rate was 6.6%. The median and - ［M（ P-P ）］ 131 （ - ） 0 100 percentile 0 100 of thyroid I activity were 42.9 35.1 47.1 Bq. When assuming that the monitoring period was ， M（ P-P ） （ - ） ， 30 days the 0 100 of single committed effective dose in thyroid gland was 0.014 0.011 0.015 mSv and the annual dose （ - ） Conclusion of internal irradiation was 0.162 0.132 0.180 mSv/a. The internal exposure of NMWs in the eight hospitals in （ ） ， Guangdong Province meets the annual effective dose limits ≤20.000 mSv/a . However it is necessary to pay attention to the internal radiation protection of NMWs and take reasonable protective measures to reduce the internal exposure risk of NMWs.