To identify genes whose alterations lead to gastric cancer, gene expression profiles have been obtained from 22 gastric cancer tissues and their surrounding gastric mucosa tissues. A total of 16 genes were differentially expressed in more than 50% of gastric cancer tissues compared with surrounding gastric mucosa tissues. Genes such as HMG-Y, fibroblast collagenase inhibitor, and osteopontin are among those that are overexpressed in over 50% of the gastric cancer tissues. Dihydrodiol dehydrogenase, ribonuclease A, and glutathione peroxidase are among those genes that are underexpressed in over 50% of the gastric cancer tissues. We identified genes that are associated with clinical phenotypes of patients with gastric cancers. Alpha-II spectrin, Na/K-ATPase and KIAA0111 are those that are enhanced in intestinal type of gastric cancer. Gene such as platelet-endothelial tetraspan antigen 3 was enhanced in highly metastatic gastric cancer tissues.