To clarify the effect of DNA methylation and histone deacetylase inhibitors on the expression of the E-cadherin gene and the invasiveness of the QBC cells, the QBC cells were separately treated with hydralazine, valproate, or combination of the two drugs. The mRNA expression of E-cadherin was examined with reverse transcription-polymerase chain reaction (RT-PCR), the protein of the gene with Western blotting. The methylation status of the promoter region of the gene was detected with methylation-specific PCR (MSP). The invasiveness of QBC cells was detected with transwell assay. It was found that the promoter region of the E-cadherin gene of QBC cells was hypermethylated. Valproate alone could not contribute to demethylation of the gene, whereas hydralazine could make them to be partly demethylated. However, the methylation status of the gene could be thoroughly reversed by using valproate and hydralazine in combination. What’s more, it was confirmed that the E-cadherin gene of QBC cells could not be transcriptionally reactivated by Valproate alone, whereas hydralazine alone could induce moderate reexpression of the gene. However, using valproate and hydralazine in combination could result in robust reexpression of the E-cadherin gene ( =0.000). Likewise, the invasiveness of the QBC939 cells was sharply decreased by treatment with two drugs in combination and slightly decreased with one drug alone. It could be concluded that the two drugs have synergistic effect on the demethylation and reexpression of the E-cadherin gene of QBC cells, and also on the reduction of the invasiveness of the QBC939 cells.