A mixed 450°C+ vacuum residue obtained from Austra-rian brown coal-derived oil with hydrogenated creosote oil was hydrogenated to elucidate the effect of catalyst mesopore diameter on the activities of Ni-Mo-γ-Al2O3 catalysts. Catalyst activities, especially for the heavy fraction in feedstock, were evaluated mainly by the conversion of 350°C+ residue to 35O°C −oil (HDC), hydrodesulfurization (HDS) and hydrodenitrogenation (HDN). These decreased in the order of HDS > HDN > HDC; whereas the deactivation rate during 50 hours on stream decreased in the order of HDC > HDN > HDS due to carbonaceous deposits on the catalyst. HDC, HDS and HDN rates per unit surface area of catalyst indicated that the HDS reaction was more strongly influenced by pore diffusion than the HDN and HDC reactions. The heavy ends in feedstock (such as asphaltenes) contained higher amounts of oxygen and nitrogen compounds. These polar compounds tended to be accumulated on the catalyst surface as the precursors for the formation of carbonaceous material deposits. The profile of carbon inside catalyst particle indicated that mesopore size of 22.6 nm might be satisfactory for reactant molecules to diffuse to the center of catalyst particle and access all of the active sites effectively.