Abstract： Objective To investigate the effects and mechanisms of 5-aza-2'-deoxycytidine (5-Aza-CdR) on endometrial cancer cell.Methods In vitro experiments of 5-Aza-CdR were done using human endometrial cancer cell line HEC-1B.Evaluation of cellular proliferation and apoptosis was ascertained respectively using trypan blue exclusion and flow cytometry.RT-PCR and methylation specific PCR(MSP) was done to detect the expression of RASSF1 A mRNA and methylation status of RASSF1 A promoter of HEC-1B cell line.Results (1) The status of cellular growth and apeptosis of HEC-1 B cell line:the growth inhibition effects of 5-Aza-CdR on HEC-1B cell line were both concentration-dependent (P ＜ 0.01) and time-dependent(P ＜0.01),as well as the apoptosis rate of HBC-1-B cell line depended on the dose of 5-Aza-CdR obviously(P ＜0.01).(2)The expression of RASSF1A mRNA of HEC-1B cell line:RASSF1A mRNA was expressed in HEC-1B cell after 5-Aza-CdR treatment,but it was undetectable before the treatment.In the groups with different concentration of 5-Aza-CdR (0.05,0.1,1,5,10 nmol/ml),the expression of RASSF1A mRNA was respectively 0.074±0.004,0.105±0.004,0.167±0.006,0.334±0.005,0.484±0.007,which were remarkably different from the group without 5-Aza-CdR(the expression of RASSF1A mRNA was 0;P ＜ 0.01).(3) The hypermethylation of RASSF1A promoter of HEC-1B cell line:the hypermethylation of RASSF1A promoter was detected in HEC-1B cell line.The status of hypermethylation was decreased after treatment with 5-Aza-CdR of 0.05,0.1,1,5 nmol/ml,meanwhile,both methylation bands and demethylation bands were observed by methylation specific PCR.After the treatment with 5-Aza-CdR of 10 nmol/ml the hypermethylation was absent absolutely.Conclusions (1) In HEC-1B cell line,5-Aza-CdR can inhibit cell proliferation and induce cell apopotosis.(2) 5-Aza-CdR can renew the expression of RASSF1A mRNA of HEC-1B cell line and reverse the hypermethylation of RASSF1A promoter.