ObjectiveTo determine the optimizing parameters in transfecting the SV-40-PED cells mediated by oligofectamine. Methods With a change of Decoy oligodeoxynucleotides(ODNs)/oligofectamine in ratio and the transfection time, the uptake rate and the mean fluorescence intensity of SP1 ODNs in the SV-40-PED cells were measured by flow cytometry to evaluate the transfection efficiencies. 4 μl oligofectamine with different concentrations of ODNs(2.5，5.0，7.5，10.0 and 12.5 μl) were put into 100 μl of DMEM without serum and antibiotics. the (SV-40-PED) cells were transfected after 20 min at room temperature. the final concentration of SP1 decay ODNs were 50，100，150，200 and 250 nmol/L. Transfection effieiency was detected at 26 h after transfection. The intracellular distribution ofSP1 ODNs was determined with a fluorescence microscope. The lactate dehydrogenase (LDH) activity in the supernatant was measured to assess the cytotoxicity.Results The uptake of SP1 ODNs into the SV-40-PED cells was significantly improved by oligofectamine. The cell appearance did not change much in the groups of 50, 100 and 150 nmol/L. In the groups of 200 and 250 nmol/L, the cell reverted after being shrinked and altered to round. At 26 h after the transfection, there was no marked change in the cell form at the concentration of 250 nmol/L. There was floatation at 48 and 72 h after the transfection. Under the fluorescence microscope, we observed fluorescent materials distributed in the cell nucleus in the successfully-transferred groups. We could see the nucleoli clearly in the groups of 200 nmol/L and 250 nmol/L. There was a ber fluorescence intensitywith a higher concentration and the fluorescent materials gathered at the cell nucleus. At the final concentration of 250 nmol/L, the LDH level was 137.12±3.92 U/L in the 72hgroup, which was significantly higher those that in the 26h group（49.61±17.13 U/L）and the 48h group（120.26±8.42 U/L）(Plt;0.01). At 26 h after the transfection, there were no statistical differences at the above LDHlevels in the different-concentration groups（Pgt;0.05）. Conclusion Transfection efficiency is the highest when the final concentration of the SP1 decoy ODNs is 250 nmol/L during the incubation of for 24 h in transfecting the SV-40-PED cells.