AIM: To investigate the expression of cyclooxygenase-2 (COX-2) in gastric cancer and its relation with the liver metastasis and prognosis. METHODS: Expression of COX-2 mRNA and protein was examined in gastric cancer and its paired substantial normal tissue by semi-quantitative reverse transcription-polymerase chain reaction and immunohistochemistry. The relation between COX-2 expression and prognosis was investigated in 195 cases. RESULTS: The expression of COX-2 mRNA in gastric cancer tissue was significantly higher than that in normal tissue in 47 cases (w=792, P<0.01). The COX-2 mRNA in pT3-4 tissue expressed higher than that in pT1-2 tissue (w=204, P<0.05). The positive expression rate of COX-2 protein was 57.9% (113/195). The COX-2 expression was significantly related to histological type, lymphnode metastasis, venous invasion and liver metastasis (P<0.05). No relation was found between COX-2 expression and invasion depth, peritoneal metastasis and International Union against Cancer TNM stage. The multiple regression analysis showed that the COX-2 expression and venous invasion were obviously associated with liver metastasis (P<0.05). However, there was no significant correlation between COX-2 immunoreactivity and prognosis. CONCLUSION: COX-2 may play an important role in the development of gastric cancer, and the over-expression of COX-2 protein may be a high risk factor for liver metastasis. A: To investigate the expression of cyclooxygenase-2 (COX-2) in gastric cancer and its relation with the liver metastasis and prognosis. METHODS: Expression of COX-2 mRNA and protein was examined in gastric cancer and its paired substantial normal tissue by The relation between COX-2 expression and prognosis was investigated in 195 cases. RESULTS: The expression of COX-2 mRNA in gastric cancer tissue was significantly higher than that in normal tissue in 47 The positive expression rate of COX-2 protein was significantly higher than that of pT1-2 tissue (w = 792, P <0.01) 57.9% (113/195). The COX-2 expression was significantly related to histological type, lymphnode metastasis, venous invasion and liver metastasis (P <0.05). No relation was found between COX-2 expression and invasion depth, peritoneal metastasis and International Union against Canc The TNM stage. The multiple regression analysis showed that the COX-2 expression and venous invasion were obviously associated with liver metastasis (P <0.05). However, there was no significant correlation between COX-2 immunoreactivity and prognosis. CONCLUSION: COX-2 may play an important role in the development of gastric cancer, and the over-expression of COX-2 protein may be a high risk factor for liver metastasis.