The rabies virus glycoprotein (RVG) peptide is known as a transfection reagent for systemic delivery of small interfering RNA (siRNA) into the brain. However, selective transfection of neuronal cells or specific brain regions remains a problem. In the present study, we show that the RVG peptide can efficiently be used as shuttle system to transfect neuronal cells with cdk4 siRNA leading to selective knockdown of cdk4 expression in vitro and in vivo. After transfection, cdk4 expression was reduced up to 75% in Neuro2A cells. Stereotactically injected RVG peptide delivered cdk4 siRNA specifically to neurons in the hippocampus, resulting in a specific knockdown of cdk4 expression up to 400 µm from the injection site. Further complexation studies of RVG peptide with larger molecules such as plasmid vectors or DNA fragments were also successfully performed and improved in vitro. Therefore, the peptide is not only a highly promising drug delivery system for siRNA and potentially other therapeutic molecules, but also a powerful tool to systematically analyze gene function in the brain under experimental settings in correlation to neurodegenerative disorders.