In the present work, NiW/Al2O3 catalyst was prepared with the use of citric acid and thermally treated at temperatures of 120, 220, 300 and 450 degrees C. It was shown that the thermal treatment at temperatures of 220-300 degrees C leads to decomposition of citrate ligands, 450 degrees C-to the almost complete removal of organic carbon. HRTEM of the sulfided catalysts showed that stacking number of WS2 increases with the increase of the thermal treatment temperature while the WS2 slab length has minimum at 220 degrees C. The results of XPS indicated that the sulfidation degree of tungsten and nickel decreases with the increase of the thermal treatment temperature. The catalyst thermally treated at 300 degrees C resulted to be most active in DBT HDS, quinoline HDN and naphthalene hydrogenation reactions. The higher activity of this catalyst in comparison with the samples thermally treated at 120 degrees C and 220 degrees C can be explained by an increased stacking degree of the sulfide WS2 slabs while maintaining a small length of sulfide slabs and by a smaller carbon content that can impede access to the active sites. The calcination at 450 degrees C leads to low activity due to the low dispersion of the active component and a decrease in the degree of sulfidation of tungsten and nickel.