In this study we evaluated the influence of medium conductivity to propidium iodide (PI) and bleomycin (BLM) electroporation mediated transfer to cells. Inverse dependency between the extracellular conductivity and the efficiency of the transfer had been found. Using 1 high voltage (HV) pulse, the total molecule transfer efficiency decreased 4.67 times when external medium conductivity increased from 0.1 to 0.9 S/m. Similar results had been found using 2 HV and 3 HV pulses. The percentage of cells killed by BLM electroporation mediated transfer had also decreased with the conductivity increase, from 79% killed cells in 0.1 S/m conductivity medium to 28% killed cells in 0.9 S/m conductivity medium. We hypothesize that the effect of external medium conductivity on electroporation mediated transfer is triggered by cell deformation during electric field application. In high conductivity external medium cell assumes oblate shape, which causes a change of voltage distribution on the cell membrane, leading to lower electric field induced transmembrane potential. On the contrary, low conductivity external medium leads to prolate cell shape and increased transmembrane potential at the electrode facing cell poles.