Through a two-step synthesis procedure, bimodal micro-mesoporous aluminosilicates, denoted as B-MASs, were synthesized by assembling preformed zeolite Y nanoclusters using a triblock polymer as template. By controlling the aging conditions of preformed zeolite nanoclusters the porosity of the B-MASs was suitably tuned. The characterization results showed that the pore walls of the mesoporous phase in the B-MASs consist of zeolite Y nanoclusters and the microporosity of the B-MASs is inherited from the incorporated nanoclusters. It was suggested that more incorporation of the well-developed zeolite nanoclusters accounts for the increasing microporosity of the B-MASs with the increasing aging temperature of the preformed zeolite nanoclusters. The incorporated nanoclusters have much shorter pore channels and mainly contribute weak Lewis acid sites to the B-MASs. The resulting bimodal micro-mesoporous materials B-MASs with mutually connected mesopores and shorter micropores showed superior catalytic properties when used for cracking heavy crude oil. (C) 2008 American Institute of Chemical Engineers.