Layered silicate/polyimide (PI) hybrid films were prepared from 4,4'-oxydianiline, 3,3',4,4'-oxydiphthalic anhydride, and chemically modified montmorillonite via an in situ intercalation polymerization pathway. The X-ray diffraction and transmission electron microscopy results indicated that the silicates were homogeneously dispersed as exfoliated layers in the PI hybrid film with 2% silicate. The mechanical properties and thermal stabilities of the PI hybrid films changed with the content of the layered silicates. The coefficient of thermal expansion and water uptake of the PI hybrid films decreased with increasing silicate contents because of the barrier effect of platelike silicate layers, which prevented the diffusion and penetration of water. The dielectric strength and electrical aging performance of the PI hybrid films could also be improved as the silicate layer highly dispersed in the films. For the hybrid PI film with 5% layered silicate, the time to failure during electrical aging exceeded 280 h, which was 2.5 times as long as that of pure PI film. (c) 2005 Wiley Periodicals, Inc.