Objective To investigate the expression of protein gene product 9.5 (PGP9.5) in human gastric cancer, and to find out the relations between its expression and carcinogenesis, invasion and metastasis of gastric cancer. Methods The expression of PGP9.5 was detected by immunohistochemistry (SP) and Western blot in 80 samples of gastric cancer and 8 samples of normal gastric tissues. Results ①Of 80 gastric cancer specimens examined, 56 cases (70.0％) showed staining with PGP9.5 in most tumor cells, whereas no PGP9.5 expression was detected in normal epithelium, which was consistent with the results of Western blot. ②The results of immunohistochemistry revealed that there were significantly correlations between the expression of PGP9.5 and the depth of invasion, the degree of differentiation, and the occurrence of lymph node metastasis (Plt;0.05), respectively; yet, there were no relation between the expression of PGP9.5 and age, gender, histopathologic type and TNM stage (Pgt;0.05). Conclusion PGP9.5 may play an important role in the invasion and metastasis of gastric cancer, and the invasion of gastric cancer could be detected by PGP9.5, which may be a useful molecular marker.