series of mesoporous molecular sieve MCM-48 with SiO2/Al2O3 ratios of 5, 25, 50, 75 and 125 was prepared and used as support for nickel and tungsten. The NiW/MCM-48 catalysts were prepared using the incipient wetness method. The hydrocracking of petroleum gas oil was carried out in a high-pressure shaking reactor at reaction temperature of 450 degrees C, contact time of 90 min and catalyst to sample ratio of 0.04 (w/w). In all prepared samples, the catalyst activity and properties were improved with increasing alumina content and found that maximum values of a total conversion and liquid product (total distillate fuels) were obtained at silica/alumina molar ratio of 50. The catalysts were characterized by number of techniques and measurements, such as TPD-TGA acidity, TGA thermal stability, BET surface area, pore volume, pore size, XRD, SEM and TEM. Product distributions were also presented and discussed. (c) 2007 Elsevier B.V. All rights reserved.