Objective: To examine the expressions of MDM2, P53 and P27 proteins in chronic esophagitis, para-cancer mucosa and esophageal carcinoma. Methods: Immunohistochemistry was used to detect the expressions of MDM2, P53 and P27 proteins in forty-seven patients suffering from chronic esophagitis and eighty-five cases of esophageal carcinoma and corresponding para-cancer mucosa. Flow cytometry((FCM) was applied to detect the quantities of these proteins expressed in fresh tissues of 48 cases of esophageal cancer and their para-cancer tissues and 24 cases of relative normal mucosa at the surface of cutting edge. Results: Immunohistochemistry results showed that the expressions of the three studied proteins were very similar in the epithelia of chronic esophagitis and para-cancer mucosa (P＞0.05). Both the qualitative and quantitative studies displayed that the P53 protein had no expression and its accumulations would appear only in the early stages of esophagus canceration while the MDM2 and P27 proteins had different degrees of expressions in cases of normal esophageal mucosa. MDM2 protein markedly increased in the advanced stages of esophageal canceration. A quantitative study showed that the expression of P27 protein had a linearity of decreasing tendency (F=9.132,P=0.002) in the course of esophageal canceration. Conclusion: Chronic esophagitis may be a precancerous lesion. Owing to the changes of the P53 and P27 proteins, we can also conclude that these occur in the early stages of esophagus oncogenesis, however the changes of MDM2 expression may occur in the advanced stage of esophageal canceration.