Hydrocraking activity of NiW supported on ultra-stable Y zeolite (USY) with different loading of active component (tungsten) and promoter (nickel) was studied in this investigation. 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 gas oil ratio of 0.04. A series of NiW/USY catalysts with different nickel (NiO = 0-10.4 wt%) and tungsten (WO3 = 0-30 wt%) concentrations were prepared using the incipient wetness method. A promoting effect of nickel is observed in all prepared samples and found that the optimum content of nickel was 5 wt%. At this loading of nickel, the values of total conversion and yield of total distillate fuels were 63.3 and 52.3 wt%, respectively. The catalyst activity and properties were enhanced with increasing the tungsten content and the maximum values of total conversion and yield of total distillate fuels were 68.7 and 51.4 wt%, respectively. The catalysts characterizations were presented in terms of SEM, TGA-TPD acidity and TGA thermal stability. (c) 2007 Elsevier B.V. All rights reserved.