Abstract: A series of Ni-Mo-W composite oxides were prepared through hydrothermal synthesis method by changing nickel precursors. The influence of nickel precursors on structure and activity of unsupported catalysts was investigated and the composite oxides were characterized by BET, XRD and SEM. Unsupported catalysts were prepared through wet-mixing-kneading method, and the fluid catalytic cracking (FCC) diesel was used as a feedstock for activity evaluation of the unsupported catalysts in a 20 ml high-pressure hydrotreating unit. The experiment results show that the composite oxides from nickel nitrate have less BET surface area and pore volume. While crystal phase of Ni-Mo-W composite oxide from basic nickel carbonate precursor tends to be amorphous, and particle size is smaller than that from nickel nitrate precursor. The experiments also reveal that surface area and pore volume of the composite oxide synthesized by basic nickel carbonate precursor are improved a lot. The activity evaluation results show that the catalyst prepared by basic nickel carbonate with larger pore volume & lower surface area performs the highest activity of hydrodesulfurization (HDS), hydrodenitrogeneration (HDN) and aromatics saturation. The sulfur and nitrogen removal rate reaches to 99.91% and 99.94%, respectively.