The design of hierarchically porous catalytic supports is considered as one of the most efficient strategies to achieve efficient mass transport and thus high catalytic performance in heterogeneous catalysis. As one of the most important catalytic supports, facile synthesis of gamma-Al2O3 with hierarchical porosities is of great industrial importance. In this paper, nest-like hollow gamma-AlOOH microspheres constructed from numerous hierarchically organized nanowires were synthesized via a template-free simple hydrothermal approach, from which hierarchically porous gamma-Al2O3 microspheres with average macropores of 900 nm, mesopores of 20 nm and a pore volume of 0.93 cm(3)/g were obtained readily. Due to their structural merits, such nest-like gamma-Al2O3 microspheres could serve as excellent catalytic support. As a demonstration, a MoNi/gamma-Al2O3 supported catalyst was prepared, which was applied for hydrodemetallization (HDM) catalysis. Compared with the catalyst prepared with the commercial gamma-Al2O3, our catalyst exhibits superior catalytic performance and longer life due to enhanced diffusion of the reactants.