Objective: The aim of this study was to explore the expression of manganese superoxide dismutase (MnSOD) in esophageal squamous cell carcinoma and its relationship with clinicopathological characteristics and its biological behavior. Methods: Immunohistochemical method (SP method), reverse transcription-polymerase chain reaction (RT-PCR) and Western blot were combined to detect the MnSOD protein and mRNA expression in 45 cases of esophageal squamous cell carcinoma and the normal tissue that was 5 cm apart from the edge of esophageal cancer lesion and without documented microscopic invasive cancer. Meanwhile, analysis was performed on the relationship between the pathological features of esophageal cancer and its biological behavior. Results: In esophageal squamous cell carcinoma and normal esophageal tissue, MnSOD protein expression was identified in 31.1% (14/45) and 86.7% (31/45) (P = 0.003), respectively, with the relative expression levels of MnSOD mRNA were 0.310 ± 0.036 and 0.482 ± 0.053 (P = 0.000). The longer the lesions and the deeper the invasion, the differentiation would become poorer and the expression level of MnSOD would get lower, indicating that the level of MnSOD protein and mRNA expression were closely related to esophageal squamous cell carcinoma in the length of lesion, depth of invasion, and degree of differentiation (P 0.05). Conclusion: The MnSOD protein and mRNA expression were both decreased in esophageal squamous cell carcinoma tissue. This may be related to the carcinogenesis and development of esophageal cancer. Detection of the expression of MnSOD would be of clinical significance in understanding the prognosis and guiding therapeutic strategy of esophageal cancer.