The signals of the transforming growth factor b (TGF-b) superfamily are conveyed through cell surface serine/threonine kinase receptors to the intracellular mediatorsknown as Smads. Activation of Smads causes their translocationfrom the cytoplasm to the nucleus, where they functionto control gene expression. The present study analyzedthe expression of Smad4 and TGF-b1 to determine theirprognostic significance in advanced gastric cancer. Of 249cases of advanced gastric cancer, 41 had invaded the muscularlayer, 114 had invaded the subserosal layer, and 94had invaded the serosa. Anti-Smad4 and TGF-b1 antibodieswere used for immunohistochemical staining. Reduced expressionof Smad4 was 75.1%, whereas positive expressionof TGF-b1 was 39.6% in gastric cancer. Smad4 expressionwas related to the depth of tumor invasion (P<0.05), andTGF-b1 expression correlated with tumor gross type (P<0.05). Postoperative survival analysis indicated that patientswho had a tumor with reduced Smad4 expression had apoorer clinical outcome than those with preserved expression (P<0.05). Furthermore, in patients with TGF-b1-positive tumors, survival rate was significantly better inpatients with preserved Smad4 expression than in those withreduced Smad4 expression (P<0.05). According to multivariateanalysis, Smad4 expression acted as an independentprognostic factor. Smad4 expression, particularly in theTGF-b pathway, is an effective predictor of outcome forpatients with advanced gastric cancer.