We have developed a simple process to fabricate high density oxide or metallic nanoparticles in the polyimide (PI) films. In this method, the polyamic acid (PAA), a precursor of PI, was reacted with a thin layer of metal film or metal powders and curing was conducted to imidize PAA to PI after soft baking to evaporate the solvent. During curing, high density nanoparticles formed in the PI film. Transmission electron microscopy showed that highly dense nanoparticles such as Cu, Cu2O, and ZnO formed in a polyimide film. The size of nanoparticles varied from 2-4 nm to larger than 10 nm. The particle size, density, and distribution depended on the curing temperature, the curing time, and the curing environment. These nanocomposites can be applied for nanofloating gate Memory devices, bistable memory devices, and optical devices utilizing the high refractive index films. The properties and applications of nanocomposites will be discussed.