Abstract: Objective To observe the effects of 5-aza-2'-deoxycytidine(5-Aza-CdR)on cell proliferation and apoptosis in ovarian cancer cell line SKOV3 and the expression of mismatch repair gene HMLH1 and HMSH2, and to investigate the potential mechanism of its antitumorigenesis. Methods Human ovarian cancer cell line SKOV3 was treated with 5-Aza-CdR(0.5 , 5 and 50μmol/L), a specific demethylation agent for 3d, and then cultured in RPMI-1640 medium for 7d.The growth of cells was observed by MTT assay. The apoptosis was analyzed by flow cytometry. The expression of HMLH1 and HMSH2 mRNA was observed by semi-quantitative reverse transcription polymerase chain reaction(RT-PCR). Results SKOV3 cells treated with 5-Aza-CdR displayed a slowed growth rate in comparison with that of the control cells, The apoptosis rate of each group were 10.59%±1.57%、17.52%±1.72%、34.10%±1.45% ,respectively ，which were markedly higher than that of control（P<0.01）.The apoptosis was also notably correlated with 5-Aza-CdR concentration（F=227.6，P<0.01）. After 0.5, 5 and 50μmol/L 5-Aza-CdR treatment, the level of HMLH1 and HMSH2 mRNA expression was increased differently, and it was significantly correlated with the concentration of 5-Aza-CdR. Conclusions 5-Aza-CdR can inhibit the proliferation and partly induce the apoptosis of human ovarian cancer cell line SKOV3 by inducing the expression of HMLH1 and HMSH2 genes ，which may be inactivated by hypermethylation. Methylation of mismatch repair genes plays an important role in the carcinogenesis and progression of ovarian cancer.