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A suspension of highly monodisperse zeolite beta nanocrystals with diameter of <40 nm was prepared from three-dimensionally ordered mesoporous-imprinted(3DOm-i)zeolite beta by a fragmentation method including sonication induced disassembly and subsequent purification by density gradient centrifugation(DGC)method.The 3DOm-i zeolite beta made within three-dimensionally ordered mesoporous(3DOm)carbon template by hydrothermal synthesis method was used as the starting material.Sonication of 3DOm-i zeolite beta results in a mixture of zeolite beta nanocrystals(ca.40 nm)from the spherical elements of the 3DOm-i zeolite and ultra-small nanocrystals(<10 nm)which were possibly from the outgrowths formed on the spherical elements of 3DOm-i zeolites.It was found that DGC method is an efficient way to separate the ultra-small nanocrystals from the suspension with using sucrose solution as a density gradient medium.Under optimized conditions,a suspension of highly monodisperse sub-40 nm zeolite beta nanocrystals was successfully prepared.