Herein, we develop a reproducible in situ crystallization route to synthesize uniform functional ZSM-5 microspheres composed of aggregated ZSM-5 nanorods and well-dispersed uniform Fe3O4 nanoparticles (NPs). The growth of such unique microspheres undergoes a NP-assisted recrystallization process from surface to core. The obtained magnetic ZSM-5 microspheres possess a uniform size (6–9 μm), ultrafine uniform Fe3O4 NPs (10 nm), good structural stability, high surface area (340 m2/g), and large magnetization (8.6 emu/g) and exhibit a potential application in Fischer–Tropsch synthesis.