Nanocrystalline NaZSM-5 zeolites with systematically varied particle sizes (15, 60, and 200 nm) were functionalized with organosilanes. Through the systematic variation of particle size and therefore external surface area of NaZSM-5, the extent of functionalization and location of functional groups were spectroscopically verified. Si-29 magic-angle spinning (MAS) NMR and Fourier transform infrared (FTIR) spectroscopy provided conclusive evidence that the silanol groups located on the external surface of NaZSM-5 were functionalized through reaction with the organosilanes. The Si-29 NMR results provided quantitative information about the extent of functionalization on NaZSM-5. A nitroxide spin label was adsorbed on the external surface of NaZSM-5 to probe the surface properties by electron paramagnetic resonance (EPR) spectroscopy. The macroscopic and microscopic properties, such as the behavior of functionalized NaZSM-5 in different solvents, and the specific surface areas were also investigated. The hydrophobicity of the functionalized NaZSM-5 was found to increase relative to the parent NaZSM-5 as expected for an organic surface coating.