SBA-15 with pore diameter greater than 10 nm was synthesized by varying the synthesis parameters and adding swelling agent hexane and inorganic salt ammonium fluoride. Direct and post synthesis modification methods were employed to incorporate aluminum in the framework of SBA-15. In the direct synthesis approach, the highest pore diameter achieved was limited to 7 nm, but post synthesis method was employed successfully to achieve high pore diameter catalysts. The pore structure of the synthesized SBA-15 did not collapse until 13 nm of pore diameter as confirmed from the small angle XRD and TEM. The prepared Ni-Mo catalysts with different pore diameters were screened for hydrotreating of heavy gas oil (HGO) in a trickle bed continuous reactor. The catalyst with 13 nm pore diameter gave highest conversion compared to other catalysts. (C) 2011 Elsevier B.V. All rights reserved.