Objective:To study the effect of PTCH1 methylation on gastric carcinogenesis and the therapeutic effect of methylation inhibitor,5-aza-2′-deoxyeytidine (5-aza-dC), for treatment of gastric cancer.Methods: The total RNAs were extracted from 10 gastric cancer tissues,their corresponding adjacent normal tissues, and gastric cancer cell line AGS.The PTCH1 mRNA expression was detected by Quantitative real-time PCR (QRT-PCR) and the methylation of the promoter was examined by methylation specific PCR (MSP).AGS cells were treated by 5-Aza-dC; the cell cycle and apoptosis were examined by flow cytometry,and the methylation level was also observed.Results: PTCH1 expression was negatively correlated with promoter methylation in gastric cancer tissues,their corresponding adjacent normal tissues, and gastric cancer cell line AGS(r=-0.591,P=0.006).5-Aza-dC treatment caused apoptosis and G0/G1 phase arrest of AGS cells,and also induced demethylation of PTCH1 and increased its expression.Conclusion: Hypermethylation of PTCH1 gene promoter region is one of the main causes of low PTCH1 expression in AGS cells.Demethylation agent 5-Aza-dC can reverse this methylation status of PTCH1 and regulate the expression of PTCH1,suggesting a role for it in gastric cancer treatment.