Background and Aim: Gastric cancer (GC) is the third cause of cancer-related death in the world with the interaction of genetic, epigenetic, and environmental factors involved in disease progression. Aberrant dysregulation of the Notch signaling pathway has been described in various tumors and in gastric cancer. Recombination signal-binding protein Jκ (RBPJ), is an important transcription regulator of the Notch target genes. RBPJ is a double-edged sword that is reported to act as an oncogene or tumor suppressor gene in different types of cancer. We have recently shown that RBPJ expression was decreased significantly (P < ۰.۰۵) in gastric adenocarcinoma. In this study, we examined the association of RBPJ expression with pathologic data. Also, we evaluated if RBPJ promoter hypermethylation is the cause of RBPJ downregulation in gastric cancer tissues.Methods: Clinicopathological consequences of RBPJ gene expression alteration of ۵۴ gastric cancer patients were evaluated. Also, CpG island methylation pattern of RBPJ gene promoter in tumoral tissues and their adjacent normal counterparts was studied using bisulfite sequencing.Results: decreased expression of RBPJ was markedly associated with stage III-IV And moderately – differentiated tumor grades (P = ۰.۰۳۷۹ and ۰.۰۴۲۴ respectively) but not with tumor lymph node metastasis (P = ۰.۱۱۷۳). No methylation changes were observed in the RBPJ regulatory region between tumoral and nontumoral tissues.Conclusion: Our findings showed that RBPJ downregulation and loss of the gene tumor suppressive may be one of the molecular changes in aggressive stage tumors and moderately – differentiated tumor grades of gastric cancer. In addition, hypermethylation is not the epigenetic mechanism that regulates RBPJ expression in gastric cancer. Further studies on RBPJ gene are needed to identify other epigenetic mechanisms that cause the gene downregulation in gastric cancer.