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Polyaspartamide-based oligo-ethylenimine brushes (PASP-EDA, PASP-TEPA, PASP-PEHA, and PASP-PEI 423) were synthesized from polysuccinimide (PSI) via a ring-opening reaction with N-Boc protected ethylenediamine, tetraethylenepentamine, pentaethylenehexamine, and linear polyethylenimine (Mn 423), respectively. PASP-TEPA, PASP-PEHA, and PASP-PEI 423 possess high buffer capacity between pH 5 and pH 7, which is comparable to that of branched PEI 25000. The cytotoxicity assay indicated that they all are less toxic than PEI 25000. At an NIP ratio of above 2, all of the four synthetic polycation brushes can condense plasmid DNA to form small sized (160-400nm) polyelectrolyte complexes with positive surface charge. The transfection of HEK 293 cells with oligo-ethylenimine brush/pRE Luc polyplexes indicated that the transfection efficiencies increased with increasing the length of oligo-ethylenimine side chains. The luciferase expression with PASP-PEHA and PASP-PEI 423 were as high as or even a little higher than that of PEI 25000. The results demonstrate that polyaspartamide-based oligo-ethylenimine brushes are a very promising class of novel polycations for highly efficient and less toxic gene delivery.