【Objective】To investigate the expression of estrogen receptor beta（ERβ）and methylation status of 5′- untranslated region in papillary thyroid carcinoma（PTC）and explore the reason for the low expression of ERβ in PTC.【Methods】Western blot and immunohistochemical staining were used to analyze the protein expression of ERβ in human normal thyroid Nthy-ori3-1 cells，thyroid papillary carcinoma BCPAP cells and tissues of normal thyroid，nodular hyperplasia and PTC. qRT-PCR was employed to detect the expression levels of ERβ mRNA（0K-1），ERβ mRNA（0N-1） and total ERβ mRNA in cells and tissues. Bisulfite genomic sequencing was performed to evaluate the methylation status of CpG islands in promoter 0K，promoter 0N and exon 0N in cells and tissues. After Nthy- ori3-1 cells and BCPAP cells were treated with 5-aza-2′-deoxycytidine（5-aza-dC），a DNA methyltransferase（DNMT）inhibitor，qRT-PCR was used to examine the expression levels of ERβ mRNA（0K-1），ERβ mRNA（0N-1）and total ERβ mRNA in the treated cells.【Results】The protein expression of ERβ in PTC cells was significantly lower than that in normal thyroid cells（P<0.01）. The cases with positive ER β expression in tissues of normal thyroid ，nodular hyperplasia and PTC were 5 ，3 and 0 ， respectively（all n=10）. The protein expression of ERβ in PTC tissues was significantly lower than that in normal thyroid tissues（P<0.05）. Compared with those in normal thyroid cells and tissues，the expression levels of ERβ mRNA（0N-1） and total ERβ mRNA in PTC were significantly reduced（P<0.01），while ERβ mRNA（0K-1）expression showed no significant difference（P>0.05）. The methylation degrees of ERβ promoter 0N and exon 0N were gradually increased in the development of PTC，while promoter 0K was unmethylated or hypomethylated in normal thyroid，nodular hyperplasia and PTC cells and tissues. 5-aza-dC treatment resulted in reexpression of ERβ mRNA（0N-1）and total ERβ mRNA in BCPAP cells but brought no change in ER β mRNA （0K-1） expression. 【Conclusions】Methylation in ER β 5′-untranslated region is correlated to the low expression of ERβ gene in PTC，especially aberrant methylation of promoter 0N and exon 0N.