Gallbladder cancer cells are stimulated by hepatocyte growth factor (HGF) in vitro and in vivo. We constructed an adenovirus vector, AdCMV.NK4, carrying the HGF antagonist HGF/NK4 (NK4) and evaluated whether or not this vector can suppress the peritoneal implantation of gallbladder cancer in a novel peritoneal injury mouse model. A human gallbladder cancer cell line (GB-d1) and human peritoneal mesothelial cells infected with the adenovirus vector produced a substantial level of NK4 protein. An invasion of GB-d1 cells was determined by a coculture with AdCMV.NK4-infected human mesothelial cells in vitro. Both the invasion and migration of GB-d1 cells were dramatically inhibited by this vector in a multiplicity of infection (MOI)-dependent manner. GB-d1 cells were intraperitoneally injected into the nude mice with peritoneal injury, followed by either AdCMV.NK4 or a control vector (AdCMV.LacZ). The incidence and the size of the metastatic tumor drastically decreased by AdCMV.NK4 ( MOI 100: n = 4, P < .0001). Real-time PCR analysis revealed a transient elevation of mouse HGF mRNA expression at the peritoneal injury sites. AdCMV.NK4 has been suggested to induce the inhibition of the implantation and growth of gallbladder cancer cells in vivo through its anti-HGF activity, and the use of NK4 gene transfer could be an effective modality for preventing peritoneal metastasis of gallbladder cancer.