βig-h3 is an extracellular matrix protein induced by transforming growth factor-β1 (TGF-β1) and involved in adhesion between cell and cell, cell and matrix. It has been proved that βig-h3 is highly expressed in human lung cancer and colorectal cancer cells, and thus it is considered to have the same effect on gastric cancer cells. This research applied histochemical staining and RT-PCR to detect the content of βig-h3 in peritoneal mesothelial cells and the content of carcino embryonic antigen (CEA) mRNA in abdominal dropsy or peritoneal washing liquid, in order to explore the relationship between the factors of peritoneal metastasis of gastric cancer and βig-h3. It was found that the positive ratio of βig-h3 in the gastric cancer group was higher than that in the benign disease group, and the positive rate of immunohistochemistry was closely related to the relative factors of peritoneal metastasis such as tumor infiltration depth, serosal types, macroscopic peritoneal metastasis, CEA mRNA, results of pleural lavage cytology (PLC) examination, etc. Research found that βig-h3 expressed distinctly in gastric cancer peritoneal metastasis, therefore, it is useful for monitoring biological behavior of gastric cancer.