In the field of gene delivery,the development of vectors with high transfection efficiency and low toxicity is of critical importance [1].Polyethylenimine (PEI) is a cationic polymer,which has been investigated for delivering antisense oligonucleotide into tumor cells.Low molecular weight PEI (800 Da) shows much lower cytotoxicity than PEI-25k,but much less activity in transfection.Previous studies have shown that hydrophobic modification of PEI to improve cell membrane interactions greatly improves its transfection activity [2].