The effect of H4SiW12O40 loading on the catalytic performance of the reduced Ni-H4SiW12O40/SiO2 catalysts for hydrocracking of n-decane with or without the presence of thiophene and pyridine is studied. The catalysts were characterized by BET, XRD, Raman, XPS, H-2-TPR, H-2-TPD, NH3-TPD and FT-IR of pyridine adsorption. It was found that addition of H4SiW12O40 to the system increases the catalytic activity and the promoting effect is a function of the H4SiW12O40 loading. The best result was obtained on 5%Ni-50%H4SiW12O40/SiO2 catalyst which shows the highest activity for hydrocracking of n-decane and excellent tolerance to the sulfur and nitrogen compounds in the feedstock. The results showed that a suitable amount of H4SiW12O40 loading on the 5%Ni/SiO2 catalyst increases the amount of both hydrogen adsorbed and Bronsted acid and Lewis acid sites on the catalyst. The high catalytic performance of the catalyst can be related to the nature of H4SiW12O40 and the proper balance between metal and acid functions. (C) 2009 Elsevier Ltd. All rights reserved.