The NiCo/Ni(OH)(2)-Co(OH)(2)/C bimetallic nanomaterials were prepared at room temperature (RT) via hydrazine hydrate reduction method. And the corresponding Ru/NiCo/Ni(OH)(2)-Co(OH)(2)/C (Ru-NiCo/C similar to uncalcined) trimetallic supported nanocatalysts were synthesized by galvanic replacement reaction. The multi-level supported nanostructure of ruthenium nanoclusters-on-NiCo-on-Ni(OH)(2)-Co(OH)(2) nanoparticles (NPs) then loaded on carbon was proved by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscope (TEM) and high resolution transmission electron microscope (HRTEM), high-angle annular dark-field scanning TEM (HAADF-STEM), STEM energy dispersive X-ray spectroscopy elemental mapping and line-scans (STEM-EDS), and high-sensitivity low-energy ion scattering spectroscopy (HS-LEIS) techniques. And the RuNiCo alloy/C and Ru@NiCo core-shell/C catalysts were obtained after the Ru-NiCo/C similar to uncalcined catalyst annealed in hydrogen at 300 degrees C and 600 degrees C, respectively. The nanostructures of the reduced RuNiCo tri-metallic supported nanocatalysts were also characterized by the above-mentioned analysis techniques. The catalytic performance of these catalysts was evaluated by naphthalene hydrogenation. The Ru-NiCo/C similar to uncalcined catalyst exhibited much more excellent catalytic performance and higher selectivity to decalin than the Ru/Ni/Ni (OH)(2)/C and Ru/Co/Co(OH)(2)/C catalysts, mainly attributed to its unique nanostructure and the positive synergistic effect among the related Ni, Co and Ru species. And Ru-NiCo/C similar to uncalcined showed good stability under mild reaction conditions (reaction temperature - 60 degrees C and hydrogen pressure - 4.48 MPa). The effect of reaction temperature on the catalytic properties of the Ru-NiCo/C similar to uncalcined catalyst was investigated in this work. However, the RuNiCo alloy/C and Ru@NiCo core-shell/C catalysts did not show any activity (yield to decalin < 0.1%) for this reaction due to their nanostructures and the absence of effective synergy effect.