Abstract: Composite molecular sieve Al-SBA-15/USY was prepared by different Al-SBA-15 samples, which was synthesized by post-alumination procedure and direct hydrothermal synthesis respectively. The composite molecular sieve samples were characterized by XRD, SEM, TEM and N2 adsorption/desorption techniques to confirm their structure having both mesoporous and microporous characteristics. Composite molecular sieve containing post-synthesized Al-SBA-15 exhibited better morphology and pore structure, having pore diameter of 4.86 nm and specific surface area of 572 m2/g; thus it seemed more suitable for treating heavy oil. Hydrocracking catalysts for enhancing middle distillates yield were prepared by such composite supports. As compared with catalyst using single USY support, the selectivity and yield of middle distillates over catalyst with Al-SBA-15/USY support (by post-synthesis) was 2 percentages and 2.6 percentages higher, respectively; besides, it is 0.6 percentages higher compared with catalyst containing Al-SBA-15 prepared by direct synthesis.