Objective：To understand promoter methylation status of thyroid hormone receptor β1（TRβ1） gene in intraductal prolifera－tive lesions and invasive ductal carcinoma of breast and to discuss its relationship with breast cancer. Methods：By methylation-spe－cific polymerase chain reaction（MSP），we detected promoter methylation status of TRβ1 gene in mammary tissues of 40 cases of in－filtrating ductal carcinoma（IDC），12 cases of usual ductal hyperplasia（UDH），8 cases of atpical ductal hyperplasia（ADH），24 cases of duetal carcinoma in situ（DCIS） and 10 cases of healthy adult women. Results：Methylation rates of TRβ1 gene were 0.0%（0/10），16.7%（2/12），37.5%（3/8），62.5%（15/24） and 80.0%（32/40） in healthy breast，UDH，ADH，DCIS，and IDC respectively. There were significant differences in methylation rate of TRβ1 gene between healthy breast and DCIS，IDC（P=0.001，P=0.000）. There was no sta－tistical difference in methylation rate of TRβ1 gene between UDH and DCIS（P=0.009）. There were statistical differences in methyla－tion rate of TRβ1 gene between UDH and IDC（P=0.000）. Conclusions：Promoter methylation of TRβ1 gene is an early event in the development of breast carcinoma and may play an important biological role in breast carcinogenesis.