We report the synthesis, crystal and band structures, and transport properties of organic conductor kappa-(ET)(2)Cu[Au(CN)(2)]Cl [ET = bis(ethylenedithio)tetrathiafulvalene], which has a triangular spin-lattice (S = 1/2) composed of (ET)(2)(center dot+) dimers and polyanions with no disorder. The anisotropy of triangular lattice t'/t = 1.19 and physical properties indicate that this material is the first ET-based quantum-spin-liquid candidate having a nearly regular triangular lattice with a disorder-free anion.