Objective: To detect the expression of annexin I in esophageal squamous cell carcinoma and precursor lesions, and evaluate its effect on the tumorigenesis. Methods: The immunohistochemistry S-P method was used to determine the expression of annexin I in 135 cases of esophageal squamous cell carcinoma, in which precursor lesions were found in some cases, and in the corresponding normal controls. Results: Of 135 cases, 35 (25.9%) were strongly positive, 60 (44.4%) were weakly positive and 40 (29.6%) negative, while in the corresponding normal controls, 129 (95.6%) were strongly positive, 6 (6.4%) weakly positive. The expression of annexin I was decreased in esophageal squamous cell carcinoma (P<0.0001), and the degree and rate of the decrease did not show correlation with age, gender, differentiation, and lymph node metastasis (P>0.05). The expression of annexin I was also decreased in the lesions of dysplasia and carcinoma in situ, with 2 (4.3%) strongly positive, 17 (37.0%) weakly positive and 27(58.7%) negative (P<0.0001). Conclusion: Annexin I may be useful in early detection of esophageal squamous cell carcinoma and in evaluation of predisposition for the risk of cancerization of precursor lesions. Objective: To detect the expression of annexin I in esophageal squamous cell carcinoma and precursor lesions, and evaluate its effect on the tumorigenesis. Methods: The immunohistochemistry SP method was used to determine the expression of annexin I in 135 cases of esophageal squamous cell carcinoma, in which precursor lesions were found in some cases, and in the corresponding normal controls. Of 135 cases, 35 (25.9%) were strongly positive, 60 (44.4%) were weakly positive and 40 (29.6%) negative, while in the corresponding normal controls, 129 (95.6%) were strongly positive, 6 (6.4%) weakly positive. The expression of annexin I was decreased in esophageal squamous cell carcinoma (P <0.0001), and the degree and rate of the decrease did not show correlation with age, gender, differentiation, and lymph node metastasis (P> 0.05). The expression of annexin I was also decreased in the lesions of dysplasia and carcinoma in situ, with 2 (4.3%) strongly positive, 17 weakly posi tive and 27 (58.7%) negative (P <0.0001). Conclusion: Annexin I may be useful in early detection of esophageal squamous cell carcinoma and in evaluation of predisposition for the risk of cancerization of precursor lesions.