Abstract: Seventy cases of gastric carcinoma and gastrosis have been studied using in situ hybridization technique with biotin labeled probs, including 48 gastric carcinoma samples, 14 chronic gastritis samples, 5 atrophic gastritis samples, one peptic ulcer and 2 normal samples. Elevated of C-myc mRNA expression was found in 29 out of 48 cases (60. 42% ) of the gastric carcinoma, and also in 6 out of 22 cases (27. 27%) of gastric disorder. The expression of C-myc gene was significantly higher in carcinoma than in benign tissues (P0. 05). The 6 cases with high level of expression of C-myc gene were all found in chronic gastritis with dysplasia (46. 15%). There were nosignificant difference between dysplasia and carcinoma.High level expression of C-myc gene was observed in the epithelium of adjacent to carcinoma (37. 5%). However, the epithelium with dysplasia showed over-expression in 15 out of 19 (78.95% ). It was much higher than that in the normal epithelium (P0. 01). In our study, the expression of C-myc gene did not correlate with the histological types of differenation of gastric carcinoma, site of tumor, serosal involvement, lymph node matastasis and peritoneal dissemination. From the result, it appears that the dysplasitic epithlium are closely related to gastric carcinoma and over-expression of C-myc gene may play a role in the carcinogenesis of this cancer.