A xenograft brain tumor model was established by the subcutaneous injection of U87MG cells into nude mice to investigate the efficacy of a non-viral vector, arginine-modified polyamidoamine dendrimer (PAMAM-R), in delivering a therapeutic gene, human interferon beta (IFN-β). We used 4′,6-diamidino-2-phenylindole staining, the terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL) assay, and the caspase-3 activity assay to determine the induction of apoptosis upon transfection with the PAMAM-R/IFN-β gene polyplex in vitro. The polyplex was injected into xenograft brain tumors. Mice treated with PAMAM-R/pORF-IFN-β exhibited a significantly smaller tumor size than control mice and PAMAM-R/pORF treated mice. Hematoxylin/eosin staining and immunohistochemistry with the endothelial growth factor receptor antibody also revealed inhibition of tumor growth. Furthermore, reverse transcription polymerase chain reaction and the TUNEL assay also verified the expression of IFN-β and induction of apoptosis in vivo. These results indicate that the PAMAM-R/pORF-IFN-β polyplex is an effective therapeutic candidate for glioblastoma multiforme due to its selective induction of apoptosis in tumor cells.