<正> Objective: To observe the series of pathological changes during the development of gastric adenocarcinoma in ulcerative rats induced by N-methyl-N’-nitro-N-nitrosoguanidine （MNNG）

and the expression profile of related on-cogenic protein. Methods: MNNG was administered in rats with ulcers due to acetic acid treatment to induce gastric cancer

and the protein expressions of ras and c-erbB2 genes in the ulcer were examined immunohistochemically along with pathological examination. Results: The incidence of gastric adenocarcinoma in the model group reaches 40% （6/ 15）

while none of the rats developed cancer in the control group with ulcers. Positive expressions of the proteins of p21ras and c-erbB2 were observed in the tissues undergoing canceration in the 6 rats of model group

but were not observed in the 5 control rats; p53 protein expression

however

failed to be detected in both groups. Conclusion: A new animal model of gastric cancer has been established in rats with gastric ulcer after MNNG trea