In order to quantify the amount of ligands or poly (ethylene glycol) (PEG) on each vector, here we developed a system in which poly-L-glutamic acid (PLG) was used as surface modifi cation loading backbone, to which one PEG (MW 5000, 10000, 20000) or epidermal growth factor (EGF) was linked. The PLG conjugates can electro-statically adsorb upon DNA/polycation complex with positive charge, and, the amount of EGF or PEG on the surface of complexes could be varied. We have made a series of complexes containing the various PLG conjugates and examined their physicochemical properties, and made a comparison of properties and transfection effi ciency between these complexes. EGF-and PEG-modifi ed complexes showed 10-25-folds higher cell transfection effi ciency than unmodifi ed complexes in medium with or without serum.