Non-viral poly(ether imine) (PETIM) dendrimers based gene delivery systems is disclosed herein, wherein the PETIM dendrimer constituted with tertiary amine branch points, n-propyl ether linkers and primary amines, with and without further functionalizations, at their peripheries, exhibits significantly reduced toxicities, over a broad concentration range. The dendrimer complexes pDNA effectively, protects DNA from endosomal damages and delivers to cell nucleus.