Intergrowth zeolites, i.e. MFI/MOR and BEA/MOR with approximate phase compositions, were hydrothermally synthesized using seed-mediated growth method. The two series of intergrowths were treated by combined alkali-acid treatments for introduction of mesoporous structure. The compositional and structural properties of both synthesized and modified materials were characterized upon the methods of X-ray diffraction (XRD), N₂ adsorption-desorption at 77 K, scanning and transmission electron microscopes (SEM/TEM), and inductively coupled plasma-atomic emission spectroscopy (ICP-AES). As a result, the changes in initial SiO₂/Al₂O₃ ratio and crystallization conditions concerning T/K, t/h and pH affected the framework Si/Al ratio and phase composition of zeolite intergrowths, and the modified intergrowths were shown to have crystalline hierarchical porous structures, especially for BEA/MOR(t) featuring of the narrower mesopore size distribution. The porous structure properties and phase composition were related to the structural stability of zeolite phases in both intergrowths. Moreover, the zeolite phases related to small primary crystal size and low framework stability were etched preferentially by alkaline media, leading to reductions in weight fraction of MFI and BEA phases. In addition, framework Si/Al ratios of modified zeolites were increased due to final acid extraction.