G250 is a tumor associated antigen that is found on > 90% of renal cell carcinoma (RCC). In order to develop a highly targeting gene vector for RCC gene therapy, G250 monoclonal antibody was prepared, purified and characterized. The antibody was chemically bound to Polyethylenimine (PEI) to form the IgG-PEI conjugate. The conjugate is capable of forming DNA complexes in the size of nano meters and with a narrow size distribution. The targeting effect and transfection efficiency were tested on five cell lines, ketr 3, Hela, ACHN, HepG2, and smooth muscle cells. The transfection was quantitatively determined by fluorescence activated cell sorting (FACS) and luciferase assay. The FACS results show that for G250 positive cells ketr 3 and Hela, the transfection efficiency of IgG-PEI are 2-fold higher than that of PEI. But for G250 negative cells, antibody modification has no effect on transfection. The expression of luciferase in ketr 3 cells which is expressed as enzyme activity is 15-fold and 61-fold higher than that in ACHN and SMC, respectively. In the presence of free antibody, the targeting effect of IgG-PEI is impaired and the transfection efficiency is normalized. It indicates that G250 antibody is an ideal targeting ligand for delivery of genes into RCC. Application of this IgG-PEI conjugate in RCC gene therapy will be of great interest.