MFI-type zeolite is an important family of materials used in today's industries as catalysts and adsorbents. Preparation of this type of zeolite material as uniform and pure crystals with sizes from tens to hundreds of nanometers are not only desired for current catalytic and adsorption processes for enhanced reaction kinetics and/or selectivity, but also much needed for some new applications, such as CO2 capture adsorbents and composite materials. However, it has been a major challenge in the field of zeolite synthesis to prepare small crystals of MFI-type zeolite over a range of Si/Al ratios with very high throughput. In this work, a gas-bubbling flow reactor was used to conduct hydrothermal growth of the zeolite crystals with controllable Si/Al ratios and crystal sizes. Distinctive, uniform ZSM-5 crystals were successfully synthesized within 2 h of reaction time, which is exceptionally short compared to the conventional synthesis process. The crystals were small enough to form a stable milk-like suspension in water. The Si/Al ratio was controlled by adjusting the growth solution composition and reaction conditions over a range from about 9 to infinity. Characterization by SEM/EDS, XRD, TEM, N-2 adsorption/desorption, and NMR spectroscopy confirmed the ZSM-5 crystal structures and revealed the presence of mesoporosity in the resulting crystals.