Background: The mechanisms of estrogen insensitivity or estrogen resistance in ovarian cancer cells are not known. Studies on regulation of the estrogen receptor (ER) gene have suggested a role for epigenetics in silencing ER expression. Materials and Methods: Cells from insensitive ovarian cancer cells, SKOV3 and HEY, were cultured with and without the DNA methyltransferase (DNMT) inhibitor, 5-aza-2'-deoxycytidine (AzaC) and the histone deacetylase (HDAC) inhibitor, trichostatin (TSA). ERβ promoter methylation was examined using bisulfite sequencing. RNA was collected for oligonucleotide array studies. Results: Cell type-specific ERβ promoter methylation was found as well as relative hypomethylation of the ERβ promoter in SKOV3 compared to HEY cells. Preferential demethylation of specific CpGs by different treatments was found. AzaC and TSA resulted in significant tumor growth inhibition and alterations in expression of numerous genes. Conclusion: The ERβ promoter is differentially methylated in ovarian cancer cells. Moreover, AzaC and TSA can inhibit ovarian cancer cell growth.