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A novel micro-micro/mesoporous aluminosilicate ZSM-5-Y/MCM-41 composite molecular sieve with a MCM-41 type structure was synthesized through a novel process of the self-assembly of CTAB surfactant micellae with silica-alumina source originated from alkaline treatment of ZSM-5 zeolite. The physical properties of the ZSM-5-Y/MCM-41 composite molecular sieve were characterized by XRD, Py-FTIR and N2 adsorption-desorption techniques. Different kinds of molecular sieves including ZSM-5, Y zeolite, Al-MCM-41, ZSM-5/MCM-41 and ZSM-5-Y/MCM-41 as cracking catalysts were investigated, using 1,3,5-triisopropylbenzene (1,3,5-TIPB) as the probe molecule. Catalytic tests showed that the ZSM-5-Y/MCM-41 composite molecular sieve exhibited higher catalytic activity compared with the microporous ZSM-5 zeolite, Y zeolite, mesoporous Al-MCM-41 molecular sieve and ZSM-5/MCM-41 composite molecular sieve under the same conditions. The remarkable catalytic activity was mainly attributed to the presence of the hierarchical pore structure and proper acidity in the ZSM-5-Y/MCM-41 composite catalyst. Meanwhile, a carbenium ion mechanism was put forward for the cracking of 1,3,5-TIPB.