Abstract: Objective To study the expression of B7-H1 in gastric mucosa of patients with gastric carcinoma， and to identify its relationship with neoplasm metastasis and prognosis. Methods Expression of B7-H1 in gastric carcinoma cell line SGC-7901 and in freshly-resected gastric mucosa including gastric carcinoma, adjacent tumor tissue and distal normal gastric mucosa were determined by flow cytometric analysis, immunochemical staining, immunofluorescence staining and Western blot. Moreover, the correlated data was analyzed statistically. And so the correlation between the expression level of B7-H1 and the patients, clinicopathological parameters was established. Results B7-H1 expression was detected in SGC-7901 cell line. And B7-H1 was found to localize in cell membrane and little cytoplasm. The positive rate of B7-H1 expression in gastric carcinoma was (13/21)62％, and it was (7/21)33％ in adjacent tumor tissue, Whereas B7-H1 was absent in distal normal gastric mucosa. The statistical analysis showed positive correlations between B7-H1 expression in gastric carcinoma and the depth of carcinoma infiltration, lymph node metastasis and pTNM stage (P < 0. 05). Conclusion B7-H1 molecule may be used as a new indicator to diagnose gastric carcinoma on early stage and to predict prognosis of this disease.