Blocking of activator protein-1 activity leads to suppression of growth factor-induced transformation. However, the role of individual components of the Jun family in this process is unclear. Over-expression of JunB has been reported to be associated with neoplastic transformation and regulation of Matrix metalloproteinase-9 (MMP-9) expression. Using cDNA microarray, we found that JunB might be one of target genes up-regulated by hepatocyte growth factor (HGF). Therefore, we tried to investigate the role of JunB in HGF-medicated cell proliferation and cell invasion in human gastric cancer cells, NUGC3 and MKN28. We verified that HGF increased JunB in time and dose-dependent manners. The JunB levels were decreased by the treatment with an NF-κB inhibitor, pyrrolidine dithiocarbamate. Down-regulation of JunB by transfecting cells with JunB-short hairpin RNAs (shRNA) inhibited MMP-9 up-regulation induced by HGF. Furthermore, transfection with JunB-shRNA repressed HGF-mediated increases in cell proliferation and cell invasion. These data suggest that JunB might be regulated through an NF-κB pathway and up-regulation of JunB induced by HGF might play an important role in the regulation of cell proliferation and cell invasion through MMP-9 expression. In conclusion, these results may contribute to the JunB-associated malignant phenotype of gastric cancers by regulating MMP-9, and serve as a novel therapeutic target for stomach cancer therapy in the future.