Spin-on pure-silica-zeolite MFI films consist of zeolite nanocrystals embedded in a compacted silica matrix of zeolite primary nanoparticles. They appear to be promising as a low-k material due to their good mechanical properties and high microporosity, parallel to their intrinsic low k-value. Results are promising but the implementation of this material is still far away. To contribute to the implementation we present a study on the final film properties depending on the zeolite MFI nanocrystal size. Different techniques are used for the characterization: Dynamic Light Scattering, X-ray diffraction, Scanning Electron Microscopy, Nitrogen adsorption, EllipsoPorosimetry using toluene and NanoIndentation. The results show a clear dependence of the film properties on the nanocrystal size. Clearly, smaller nanocrystals provide better homogeneity, smaller pore size and higher mechanical properties. However, due to the hydrophilicity of the silica matrix lower k-values are only obtained for larger zeolite nanocrystals which provide with higher crystallinity in the films.