Polyphenols are natural antioxidants that are thought to contribute to prevention of cardiovascular disease and malignancy. Although many studies have been carried out to investigate the chemopreventive role of flavonoids, less attention has been focused on phenolic acids. In this study, the aim was to investigate the effect of phenolic acids found abundantly in vegetables, i.e. gallic acid (GA), caffeic acid (CA) and protocatechuic acid (PCA), on the inhibition of gastric adenocarcinoma (AGS) cell metastasis. The results showed 0.01 mM GA induced the same level of cell toxicity as 4.0 mM PCA. Using wound-healing assay and Boyden chamber assay, GA had potent inhibitory effects on AGS cell migration. The expression of MMP-2/9 of AGS cells was inhibited by 2.0 μM of GA. It is possible that the suppressive effect of GA on MMP-2/9 might involve the inhibition of NF-κB activity. Multiple proteins involved in metastasis and the cytoskeletal reorganization signal pathway, including Ras, Cdc42, Rac1, RhoA, RhoB, PI3K and p38MAPK, were also inhibited by GA. Furthermore, immunoreactivity assay of cytoskeletal F-actin demonstrated a significant inhibitory effect of GA treatment. In conclusion, GA may have the potential to be an effective agent for prevention and treatment of gastric cancer metastasis.