Abstract: Objective: To investigate the effect of 5-Aza-2'-deoxycytidine (5-Aza-CdR) on human leukocyte antigen C (HLA-C) expression and the relationship with DNA methyltransferase 1 (DNMT1) in gastric cancer cells.Methods: The gastric cancer cells BCG823 cultured in medium containing 10 μmol/L 5-Aza-CdR (final concentration) were as experiment group.The untreated gastric cancer cell were as control group.The transcripts of HLA-C and DNMT1 genes were detected by semi-quantitative reverse transcription-PCR (RT-PCR).The methylation level of HLA-C was analyzed by methylation-specific PCR (MSP).Results: The expression of DNMT1 mRNA in BGC823 cells treated with 5-Aza-CdR were obvious less than in untreated cells.The DNA hypermethylation in CpG island of HLA-C gene was reversed and leaded to up-regulation of HLA-C transcripts.There was the statistical significance between the control and experiment group in the expression of HLA-C mRNA analyzed by Gel-Pro Analyzer (P<0.01).Conclusions: 5-Aza-CdR treatment can lead to DNA demethylation of HLA-C through inhibiting the expression of DNMT1,and then up-regulating the expression of HLA-C mRNA.