Our study used protein array technology to analyze the expression status of various activated receptor tyrosine kinases (RTKs) in gastric carcinoma; then, we sought to discover an effective therapeutic receptor tyrosine kinase for this disease and investigated the anti-tumor mechanism of the therapeutic RTK. In addition to the expressions of activated RTKs in human gastric cancer and adjacent normal mucosa, the expression of activated RTKs in gastric cancer cell lines, MKN74, MKN45, MKN7 and MKN1, were also studied. The RTKs activated in gastric cancer tissue are EGFR, ErbB2, FGFR1, FGFR2alpha insulin R, and EphA4. Among the RTKs activated in gastric cancer tissues, EGFR and ErbB2 were also activated in all gastric cell lines examined in this study. A subsequent in vitro experiment using subcutaneous gastric cancer-bearing athymic nude mice demonstrated that the ErbB2-targeting drug trastuzumab markedly suppressed the growth of gastric cancer. Moreover, using an angiogenesis protein array, the expressions of Ang I, FGF-alpha, FGF-beta TGF-beta and IL-8 in MKN74 xenograft tumors were found to be significantly reduced by treatment with trastuzumab, indicating that trastuzumab may inhibit the expression of angiogenic molecules in MKN74 cells in vivo. These data suggest that ErbB2 is activated in gastric cancer, and the ErbB2-targeting drug trastuzumab may be related to the reduction of Ang 1, FGFalpha, FGFbeta, TGFalpha and IL-8.