Multi-wall carbon nanotubes (MWCNTs) with a diameter of 20-30 nm were dispersed as a conductive phase into yttria stabilized tetragonal zirconia polycrystalline (3Y-TZP) to add electrical conductivity. The 3Y-TZP/MWCNT nanocomposites were fabricated by pressureless sintering under inert atmosphere. Electrical conductive function was successfully introduced by small amount of CNT addition. Critical volume fraction of the conductive phase for the percolation was analyzed and was found to be 0.390 vol% of CNT, which was much smaller than that for nano-sized carbon black dispersed 3Y-TZP (2.55 vol%). Microstructural investigation revealed that dispersed CNTs formed continuous 3-dimensional nano-network within the 3Y-TZP matrix, that contributed to the excellent conductive properties. Fracture strength was not improved much, while fracture toughness was increased by the CNT addition, due mainly to its crack bridging and/or pull-out mechanisms. It was considered that the use of anisotropic nano-sized conductive phase is advantageous to obtain electrically functionalized nanocomposite ceramics.