Electropermeabilization is one of the non-viral methods successfully used to transfer genes into living cells invitro and in-vivo. Although this method shows promises in the field of gene therapy, very little is known about the basic processes supporting plasmid DNA transfer. In contrast to small molecules that have direct access to the cytoplasm, plasmid DNA forms a long-lasting complex with the permeabilized membrane. The present letter reports the semi-quantitative analysis of the effect of electric pulse intensity on plasmid DNA/membrane interaction at the single-cell level using fluorescence microscopy. The raising of electric field intensity induces an increase in the cellular perimeter of plasmid DNA/membrane interaction and in the total number of plasmid DNA complexes. The increase in the perimeter of plasmid DNA/membrane interaction is in good agreement with the theoretical perimeter of membrane permeabilization. This theory easily explains the quantitative increase in plasmid DNA and gives explanations for the success of electro-mediated gene delivery.