The concept of pseudomorphic transformation was used to transform amorphous mesoporous silica beads with different size (20, 50 and 75 μm) into hierarchical MFI-type zeolite beads composed of ZSM-5 nanosheets. The beads were synthesized under hydrothermal conditions with and without mechanical stirring at different temperatures and treatment times. The influence of the different synthesis parameters was investigated by X-Ray Diffraction, Scanning Electron Microscopy, Transmission Electron Microscopy, X-Ray Fluorescence, Nitrogen adsorption-desorption measurements, 27Al solid-state Nuclear Magnetic Resonance, Energy-Dispersive X-Ray analysis and Thermogravimetric analysis. Well-crystallized 20 μm ZSM-5 nanosheets beads similar in size and shape to the original mesoporous amorphous silica beads were obtained after a hydrothermal treatment at 150 °C for 5 days in a tumbling oven and 2 days in static conditions at 120 °C. The influence of the bead size on the pseudomorphic transformation was studied in order to prepare well-crystallized ZSM-5 nanosheets beads of 50 and 75 μm. Results showed that the required time of static treatment at 120 °C increases when the size of the parent silica spheres increases. This is explained by the fact that crystallization starts from the outer bead surface toward the center.