Hierarchical porous particles aggregated from primary zeolite Y nanocrystals were hydrothermally synthesized using a three-stage variable-temperature program without adding any organic addictives and seeding crystals. The as-synthesized samples were characterized using powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDXS), N₂ sorption, particle size analysis and Fourier transform infrared (FT-IR) spectroscopy. The significantly broadened XRD peaks associated with zeolite FAU structure indicated that primary crystals were very small. SEM images showed that the zeolite particles are composed of very uniform zeolite Y nanocrystals in the size range of 20-80 nm. TEM revealed the intergrowth and random packing characteristics of the primary zeolite Y nanocrystals. FAU structure of the as-synthesized samples was further conformed by FT-IR result. Interestingly, the particle size of the aggregates could be easily controlled by varying the alkalinity of the precursor without notably changing the primary size of zeolite Y nanocrystals. N₂ adsorption result showed the zeolite aggregates contained disordered micro- and mesopores and had large surface area arising from zeolite Y nanocrystals. The hierarchical porous particles are mechanically strong, and they remain intact after ultrasonication for several hours.