A pure silica zeolite film was formed by use of hydrothermally crystallized zeolite nanoparticles in a porous silica precursor. The effects of silylation hardening by tetramethylcyclotetrasiloxane (TMCTS) vapor treatment on the electrical characteristics of pure silica zeolite films were investigated. The results from Fourier-transform-IR spectroscopy indicated that the O-H bond decreased by zeolite formation, resulting in the decrease of the leakage current by 1/10. Silylation hardening by TMCTS vapor treatment could reduce the leakage current by 4 orders of magnitude due to the reduction of Si-OH and O-H bonds. The elastic modulus of 5.18 GPa and the dielectric constant of 1.96 were achieved simultaneously by silylation hardening. Consequently, the electrical and mechanical characteristics of the pure silica zeolite film as well as the time dependent dielectric breakdown lifetime were improved.