The low transfection efficiency of polycations is still a major problem for successful gene therapy. To address this issue, in this study, hydrophilic poly(vinyl pyrrolidone)-graft-poly[2-(N,N-dimethylamino)ethyl methacrylate] (PVP-g-PDMAEMA) and amphiphilic poly(vinyl pyrrolidone)-graft-poly[2-(N,N-dimethylamino)ethyl methacrylate]-block-poly(methylmethacrylate) (PVP-g-PDMAEMA-b-PMMA) were synthesized via the atom transfer radical polymerization (ATRP) method, and their properties as gene vectors were investigated subsequently. PVP-g-PDMAEMA formed random coils in water and PVP-g-PDMAEMA-b-PMMA self-assembled into spherical core–shell micelles with a very low critical micelle concentration of only 6.3 × 10−3 mg mL−1. PVP-g-PDMAEMA-b-PMMA/pDNA polyplexes demonstrated an excellent gene transfection efficiency, which showed not only much higher gene transfection efficiency than PVP-g-PDMAEMA/pDNA polyplexes, but obviously surpassed 25k PEI at low N/P ratio around 3 on 293T cell lines. Hence, the results suggested that PVP-g-PDMAEMA-b-PMMA could be a highly efficient gene vector.