To investigate cyclooxygenase- 2(Cox-2) protein expression in esophageal cancer and precancerous lesions. Methods: One hundred twenty biopsy specimens from esophageal carcinoma and 113 from patients with esophageal premalingnant lesions, 27 from individuals with normal esophageal mucosa and 3 from Barrett’s esophagus were examined for Cox-2 protein expression by immunohistochemistry. Results: Cox-2 protein was not observed in normal esophageal squamous and glandular epithelium, hyperplasia from mild to severe dysplasia lesions and carcinoma in situ. Positive Cox-2 protein expression was found in 4 of 60 specimens of invasive squamous-cell carcinomas, 21 of 30 specimens of esophageal adenocarcinomas and in 3 of 3 Barret’s esophageal tissues. Conclusion: The Cox-2 protein expression may be associated with the development of the esophageal adenocarcinomas but not esophageal squamous-cell carcinomas.