OBJECTIVE To investigate the cytidylyl phosphate guanosine (CpG) islands methylation status of E-cadherin (E-cad) promoter region in human ovarian carcinoma cell lines (ES-2,3AO,SKOV3), and the effect of 5-azacytidine-2'-deoxycytidines (5-Aza-CdR) on the cell proliferative ability, invasion and the expression of E-cad protein. METHODS Methylation specific PCR (MSP) was used to detect CpG islands methylation status of E-cad promoter region in ES-2,3AO and SKOV3 cell lines. After treated with different concentrations of 5-Aza-CdR, morphological changes of cell lines were observed under microscope. The proliferative ability was evaluated by methyl thiazolyl tetrazolium (MTT) assay. E-cad protein expression was detected by western-blot and cellular invasion was investigated by 24-well matrigel invasion chambers. RESULTS Hypermethylation status of CpG islands of E-cad promoter region was observed in ES-2 and SKOV3 cell lines, but not in 3AO cell lines. After treated with 5-Aza-CdR (0.1, 1.0, 10.0 micromol/L), ES-2 and SKOV3 cell lines displayed morphological evidence of differentiation. 5-Aza-CdR was found to decrease proliferation as evidenced by cell growth curve , to increase the level of E-cad protein expression (P < 0.01), and effectively inhibit the ability of cell invasion (P < 0.01). CONCLUSIONS CpG hypermethylation is an important mechanism of E-cad gene inactivation in ES-2 and SKOV3 cell lines. 5-Aza-CdR be found to inhibit proliferation and invasion, and increase the expression of E-cad probably by the inhibition of hypermethylation.