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 tothat of branched PEI 25000. The cytotoxicity assay indicated that they all are less toxic than PEI 25000. At anN/P 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 witholigo-ethylenimine brush/pRE Luc polyplexes indicated that the transfection efficiencies increased with increasingthe length of oligo-ethylenimine side chains. The luciferase expression with PASP-PEHA and PASP-PEI 423were as high as or even a little higher than that of PEI 25000. The results demonstrate that polyaspartamidebasedoligo-ethylenimine brushes are a very promising class of novel polycations for highly efficient and lesstoxic gene delivery.