USY zeolites were modified by zirconium, phosphorus and both zirconium and phosphorus, and the corresponding catalysts were prepared for hydrocracking of vacuum gas oil. The results showed that Zr-modified USY enhanced W species dispersion on catalyst surface, weakened interaction of W species with support and improved W species reducibility, leading to formation of highly stacked WS2 slabs and higher sulfidation degree of W species, which was favorable for the enhancement of hydrogenation activity. The influence of the modification with zirconium and phosphorus on these properties of catalyst was more pronounced than that of zirconium or phosphorus modification because of the synergistic action of phosphorus and zirconium. The catalyst containing Zr-USY had slightly lower hydrocracking activity than that containing USY owing to a diminution of acid sites, but presented obviously greater middle distillate selectivity arising from the improvement of hydrogenation activity. The middle distillate selectivity on catalyst containing Zr-P-USY was higher than that on catalysts containing Zr-USY or P-USY, corresponding to its more effective catalyst properties. (c) 2012 Elsevier B.V. All rights reserved.