Objective:To identify differentially expressed proteins related with malignant transformation of esophageal squamous cell carcinoma (ESCC) using proteomic analysis. Methods:Two-dimensional gel electrophoresis (2-DE) and matrix-assisted laser desorption/ionization timE-of flight mass spectrometry (MALDI-TOF-MS) in combination with protein database searching were used to determine and identify differentially expressed proteins in esophageal cancer cell lines (EC1, EC18, and EC109) and immortal cell line (NECA-E6E7-hTERT). Western blotting and immunocytochemistry were used to verify the differential expression of annexin 2 in esophageal cancer cell lines and immortal cell line (NECA-E6E7-hTERT). Real-time fluorogentic quantitative PCR(RFQ-PCR) was performed to analyze the expression level of annexin A2 mRNA.Results: A total of 15 differentially expressed proteins were identified with more than 5 folds difference. Among them three proteins were down-regulated and 12 proteins were up-regulated. Western blotting and immunocytochemical analysis verified the down-regulation of annexin A2 protein in ESCC cell lines. However, differential expression pattern of annexin A2 mRNA was not consistant with its protein expression in ESCC cell lines and immortal cell line (NECA-E6E7-hTERT). Conclusion:The findings provide important clues for identifying the candidate biomarkers for high-risk population screening and early diagnosis of ESCC. Post-translative regulation/modification contributes to the down-regulation of annexin A2 protein.