We have shown that ECRG4 suppressed Fas‐induced apoptosis in Jurkat cells. ECRG4 mRNA expression was ubiquitously detected in normal adult human tissues, suggesting that ECRG4 plays a major role in human tissues. ECRG4 mRNA expression was down‐regulated in tumor cells. Expression of ECRG4 suppressed cell growth. We established an anti‐ECRG4 monoclonal antibody. Our immunohistochemical analysis demonstrated that ECRG4‐positive cells tended to be distributed in the region that was negative for Ki‐67 in esophageal squamous cell carcinoma tissues. There was a significant inverse correlation between ECRG4 expression and Ki‐67 labeling index in esophageal squamous cell carcinoma. This study provides the first functional evidence for an association of endogenous expression of ECRG4 with cell proliferation. ECRG4 is a candidate tumor suppressor gene that might be involved in the proliferation of esophageal squamous cell carcinoma.