We designed a novel type of arginine-rich dendrimer, with a structure based on the well-defined dendrimer, polyamidoamine dendrimer (PAMAM). Further characterization was performed to prove that the polymer is a potent nonviral gene delivery carrier. The primary amines located on the surface of PAMAM were conjugated with L-arginine to generate an L-arginine-grafted-PAMAM dendrimer (PAMAM-Arg). For comparison, an L-lysine-grafted-PAMAM dendrimer (PAMAM-Lys) was also generated and compared as a control reagent. The polymers were found to self-assemble electrostatically with plasmid DNA, forming nanometer-scale complexes. From dynamic light scattering experiments, the mean diameter of the polyplexes was observed to be around 200 nm. We used PicoGreen reagent as an efficient probe for assaying complex formation of polymers with plasmid DNA. The complex composed of PAMAM-Arg/DNA showed increased gene delivery potency compared to native PAMAM dendrimer and PAMAM-Lys. The cytotoxicity and transfection efficiencies for 293, HepG2, and Neuro 2A cells were measured by comparison with PEI and PAMAM. In addition, transfection experiments were performed in primary rat vascular smooth muscle cells, and PAMAM-Arg showed much enhanced transfection efficiency. These findings suggest that the L-arginine-grafted-PAMAM dendrimer possesses the potential to be a novel gene delivery carrier for gene therapy.