AIM: To observe the expression of cyclooxygenase-2 (COX-2) and to investigate the association between COX-2expression and infection with cytotoxic-associated gene A( cagA) positive strair Helicobacter pylori ( Hp) in humangastric cancer, and subsequently to provide fresh ideas forthe early prevention of gastric cancer.METHODS: 32 Specimens of gastric cancer andcorresponding adjacent normal gastric mucosa were obtainedfrom patients who had undergone surgical operations ofgastric cancer. All the samples including 1 case of stomachmalignant lymphoma and 31 cases of gastric adenocarcinomawere confirmed by pathology diagnosis. The expression ofCOX-2 in 32 specimens of gastric cancer and correspondingadjacent normal gastric mucosa was quantitativelydetermined and analyzed with Flow Cytometry, and the levelsof COX-2 protein were compared between specimens withcagA+ Hp infection and those without cagA+ Hp infection.The cagA gene in 32 specimens of gastric cancer wasdetected bypolymerase chain reaction (PCR) method.RESULTS: Twenty-seven of 32 (84 %) specimens of gastriccancer showed over-expression of COX-2, compared withthe adjacent normal gastric mucosa. cagA+ gene weredetected from 19 specimens of gastric cancer, but not fromthe other 13 specimens. The levels of COX-2 protein in 19specimens of gastric cancer with cagA+ Hp infection (thenumber of positive cells was 73.82±18.2) were significantlyhigher than those in the 13 specimens without cagA+ Hpinfection (the number of positive cells was 35.92±22.1).CONCLUSION: COX-2 is overexpressed in gastric cancerand cagA+Hp infection could up-regulate the expression ofCOX-2 in gastric cancer in human. There may also existanother way or channel to regulate the expression of COX-2 in gastric cancer in addition to cagA+Hp infection.Therefore, applying COX-2 selective inhibitors could be aneffective and promising way to prevent gastric cancer.