A reliable, low-cost, and highly efficient nonviral gene delivery system using lower molecular weight polyethylenimine (LMW-PEI) is provided. LMW-PEI was linked to an expressing plasmid with green fluorescence protein gene (gfp), the transfection activity mediated by PEIs were examined in the CM7721 cell line and the skin tissue of mouse, respectively. The cytotoxicity of PEIs, the localization and continuance time of gfp expressed in the skin tissue of mouse were also studied. Results showed that the transfection rate of gfp mediated by LMW-PEI in the CM7721 cell line was about 55%. However, with the increasing PEI molecular weight, the cytotoxicity of PEI increased, but its transfection activity decreased. The tissue transfection results showed that LMW-PEI induced a significant expression of the gfp in the cells of hair vesicle and sweat gland of mouse skin tissues following transfection of 24 h, and the expression of gfp lasted 7～9 d. When the tissue of mouse was treated with retinoic acid and nitrogenous ketone, respectively, gfp was transferred to the granule layer of mouse skin tissue. The LMW-PEI described here is a new, highly efficient vector; it would be a useful nonviral vector for gene delivery technology.