Comb-shaped polymeric vectors (SS-PGEADMs) consisting of ethanolamine/cystamine-functionalized poly(glycidyl methacrylate) (SS-PGEA-NH2) backbones and bioreducible poly((2-dimethyl amino)ethyl methacrylate) (PDMEAMA) side chains were prepared by a combination of the ring-opening reaction and atom transfer radical polymerization (ATRP). The SS-PGEA-NH2 backbones, which were prepared via the ring-opening reaction of the pendant epoxide groups of poly(glycidyl methacrylate) with the amine moieties of ethanolamine/cystamine, possess plentiful flanking secondary amine and hydroxyl groups and some flanking disulfide bond-containing cystamine derivatives. The primary amine groups of the cystamine derivatives were activated to produce bromoisobutylryl-terminated SS-PGEA (SS-PGEA-Br) as multifunctional initiators for subsequent ATRP of DMAEMA. The resultant disulfide-linked short PDMEAMA side chains possess pendant tertiary amine groups and are biocleavable. Such SS-PGEADMs can effectively condense pDNA. The cytotoxicity of SS-PGEADMs could be controlled by adjusting the grafting amount of PDMEAMA side chains. In comparison with the pristine SS-PGEA-NH2, the moderate introduction of PDMEAMA side chains can further enhance the gene transfection efficiency in different cell lines. The present approach to well-defined comb-shaped vectors with multifunctional groups could provide a versatile means for tailoring the functional structures of advanced gene/drug vectors.