The aim of this study was to determine whether the risk of second primary breast cancer (SPBC) is increased in thyroid cancer patients treated with radioactive iodine (RAI). We searched the MEDLINE, EMBASE, and the Cochrane Library and Chinese database for studies that reported the risk of SPBC in thyroid cancer patients treated with RAI and patients not treated with RAI. Two independent reviewers screened citations and reviewed full-text papers. A meta-analysis was carried out using the Review Manager software. Six cohort studies (three from Europe, one from America, and two from east Asia) with 17,914 patients were included in this review. The relative risk of SPBC in thyroid cancer survivors treated with RAI was 0.61 (95% confidence interval 0.47-0.79) relative to thyroid cancer survivors not treated with RAI. The risk of SPBC in thyroid cancer survivors treated with RAI is not increased compared with thyroid cancer survivors not treated with RAI.