The fixed rabies virus (RV) strain, Nishigahara, kills adult mice after intracerebral inoculation, whereas the chicken embryo fibroblast cell-adapted strain Ni-CE causes non-lethal infection in adult mice. We previously reported that the chimeric CE(NiP) strain, which has the phosphoprotein (P protein) gene from Nishigahara strain in the genetic background of Ni-CE strain, causes lethal infection in adult mice, indicating that the P gene is responsible for the different pathogenicities of Nishigahara and Ni-CE strains. Previous studies demonstrated that RV P protein binds to the interferon (IFN)-activated transcription factor STAT1, and blocks IFN signaling by preventing its translocation to the nucleus. In this study, we examine the molecular mechanism by which RV P protein determines viral pathogenicity by comparing IFN-antagonist activities of Nishigahara and Ni-CE P proteins. The results, obtained from both RV-infected cells and cells transfected to express P protein only, show that Ni-CE P protein is significantly impaired for its capacity to block IFN-activated STAT1 nuclear translocation and, consequently, inhibits IFN signaling less efficiently than Nishigahara P protein. Further, it was demonstrated that a defect in the nuclear export of Ni-CE P protein correlates with a defect in its ability to cause the mislocalization of STAT1. These data provide the first evidence that the capacity of the RV P protein to inhibit STAT1 nuclear translocation and IFN signaling correlates with the viral pathogenicity.