Lithium-taeniolite films (9-12 mu m) were soaked in methyltrimethoxysilane (MTMS) for periods shorter than 48 h at room temperature. The MTMS was hydrolysed by water contained in the film, and the resulting polymer buried gaps in the film. The polymer existed also in the vicinity of the film surface. The taeniolite particles constructing the film seem to be bound by the polymers. Mechanical properties of the films after the MTMS treatment showed five times larger modulus of tough ness than that of the untreated film. An impurity of fine LiF particles in the film lowered tensile strength and modulus of toughness.