Peritoneal dissemination is one of the main causes of death in gastric cancer patients. Our previous study demonstrated that peritoneal fibrosis induced by transforming growth factor-β1 (TGF-β1) may provide a favorable environment for the dissemination of gastric cancer. The role of Smad3 in the development of dermal fibrosis, subcapsular cataract, and peritoneal fibrosis has been reported. However, the potential role of Smad2 in the development of fibrosis is unclear. The objective of this study was to determine the effect of Smad2 in peritoneal fibrosis, induced by TGF-β1, on dissemination of gastric cancer. Here we demonstrate that TGF-β1 significantly stimulated the expression of collagen III and fibronectin in mesothelial cells through the Smad2 signal transduction pathway, but knockdown of the Smad2 gene by silencing siRNA partially inhibited these effects. This inhibition was associated with a depressed adhesion and invasiveness of gastric cancer cells. We conclude that peritoneal fibrosis induced by TGF-β1 is dependent on Smad2 signaling and may provide a hospitable environment for carcinomatosis.