Abstract: Objective To investigate the relationship between mast cell infiltration and the development and metastasis of gastric carcinoma. Methods Alcian blue-Safranin O staining and image analysis system were employed to observe,classify and quantify the mast cells in 74 gastric carcinoma specimens. Results Mast cells resided predominantly in the marginal area of the tumor and most of them were mature type,active and capable of discharging granules into the cytoplasm.The mast cells in the marginal area of the tumor were significantly more numerous than those in the matrix of the tumor (P<0.01) and there was a positive correlation between them (r=0.303,P<0.01).The density of the mast cells was inversely correlated to the depth of tumor invasion and the number of lymph node metastasis. Conclusions Mast cell infiltration in the matrix of the tumor plays an important role in preventing the invasion and metastasis of gastric cancinoma possibly by release of heparin and other bioactive substances.Mast cell quantity in the marginal area of the tumor may serve as an indicator for prognostic assessment of gastric carcinoma.