Hierarchical Beta nanozeolites with the properties of both Beta nanozeolite and mesoporous material were prepared by two different methods: (1) Direct Hydrothermal Method (DHM) by the assembly of nanocrystals of preformed Beta seeds in the presence of the surfactant P123 under hydrothermal conditions, (2) Acidification of Beta seeds suspension (without the use of the mesopore directing agent). For the two methods, the effect of crystallization time of Beta nanozeolite precursor (seeds) was studied: 6, 12 and 24 h. The obtained materials were characterized using nitrogen sorption measurements, thermogravimetric analysis (TGA), X-ray diffraction (XRD), transmission electron microscopy (TEM), ammonia Temperature Programmed Desorption (NH3-TPD) and adsorption/desorption of pyridine monitored by FTIR. The characterization results show that acidification of Beta seeds suspension leads to best structured nano-Beta (Beta nanoparticles). However, with the DHM method physical mixtures of Beta nanoparticles and mesoporous SBA-15 phases were obtained. The m-xylene isomerization/disproportionation reaction in gas-phase was carried out over all the synthesized solids in order to explore their catalytic properties. It was found that the m-xylene conversion and isomerization/disproportionation ratio were closely related to the crystallization time of Beta zeolite precursors, mesopores creation in hierarchical Beta zeolite nanoparticles and the method used to produce the extra meso-porosity.