To reveal the proteomic background of lymph node metastasis (LNM) in gastric cancer, we performed a proteomic study of tumor and matched nontumor tissues obtained from surgically resected specimens of 22 patients with or without LNM. Using laser microdissection, we recovered specific populations of tumor and nontumor cells. We used two-dimensional difference gel electrophoresis with a large format electrophoresis apparatus to obtain protein expression profiles consisting of 3228 protein spots, and we classified them according to their expression pattern. We found that macrophage-capping protein (CapG) was up-regulated in the tumor tissues of patients with LNM, whereas it showed an equivalent expression level between nontumor and tumor tissues of patients without LNM. It was reported that CapG associated with invasion and metastasis in various malignancies. However, CapG was not investigated in gastric cancer until our study. Western blotting of the laser microdissected tissue samples confirmed up-regulation of CapG in the tumor tissues of patients with LNM. Functional assays demonstrated that CapG promoted tumor cell invasion, but not cell proliferation. The association between CapG expression and LNM is a novel finding in gastric cancer. Further investigation for a prognostic utility of CapG may lead to a risk stratification therapy for gastric cancer.