We developed a small implantable type of bipolar cuff microelectrode using new electro-conductive rubber material, which was able to applied to measure renal sympathetic nerve activity in the rat (Jpn J Physiol 53:61-64, 2003). In the present study, we improved the physical and electrical characteristics of the implantable electrode substantially in the following aspects; 1) electrode material, 2) reduction in electrode impedance, and 3) shielding with electro-conductive tubing shunted to the earth. The cylindrical structures, which were made of electro-conductors and nonconductors, were made with medical grade silicone rubber and firmly fixed each other. The impedance of the silicone electro-conductors was small enough to measure sympathetic neural discharge with a good signal-to-noise ratio. A pair of Teflon-coated wires were firmly fixed to the electro-conductors. The outer surface of the electrode was coated with silicone gel for insulation. A renal nerve bundle was inserted into the center hole of the electrode (diameter, 0.15 mm) through a slit with help of sutures to open the slit. Renal sympathetic nerve activity, which was verified by sympathetic ganglionic blockade, could be recorded using the new type of implantable electrode. In conclusion, we have improved the physical and electrical properties of the implantable cuff electrode so as to measure sympathetic neural discharge more easily. [Jpn J Physiol 55 Suppl:S193 (2005)]