Abstract: Objective: To investigate the relationship between gastrin and cyclooxygenase-2(COX-2) expression andproliferation, differentiation and malignant transformation of colorectal adenomas. Methods: The expression of gastrin,COX-2 and Ki-67 was detected by immunohistochemistry in 68 samples of colorectal adenoma, 10 samples of non-ade-noma and 15 samples of normal colonic mucosa. Those patients with inflammatory bowel disease, familial polyposis coli ora history of taking non-steroidal anti-inflammatory drugs (including low-dose aspirin) or glucocorticoid and proton pumpinhibitors were excluded. Results: The expression of gastrin and COX-2 was higher in adenoma tissues (P<0.01), especial-ly in villous adenoma, severe dysplasia and polyps with malignant transformation. Correlation analysis showed that gastrinand COX-2 expression levels were significantly related to pathological type and dysplasia grade of polyps (P<0.01). Fur-thermore, a positive correlation between COX-2 and gastrin expression (r=0.67, P<0.01) was found. The expression of Ki-67 was significantly higher in patients with expression of both gastrin and COX-2 than in patients without expression ofgastrin or COX-2 (P<0.01). Conclusion: Increased expression of gastrin and COX-2 is involved in the mechanisms ofgrowth and malignant transformation of adenoma, and it may play an important role in the progression of colorectal adeno-ma. Gastrin may induce COX-2 expression and co-stimulate cell proliferation during the growth and malignant transfor-mation of adenoma.