ABSTRACT:The polyamic acid (PAA) solutions were blended directly with a commercial nanoscale colloidal silica sol, and converted to polyimides (PIs)/silica nanocomposite films. Polyamic acid was prepared from the reaction of Pyromellitic anhydride (PMDA), 4,4-oxydianiline (ODA). The nanoscale silica particles were dispersed well in PI from scanning electron microscopy (SEM) and the nanocomposite films showed a moderated optical transparency for up to 30 wt % of silica content. These PI/silica nanocomposite films exhibited better mechanical properties, higher glass transition temperature (T g ), better thermal stability and lower coefficient of thermal expansion (CTE) with increasing silica content from tensile tests, dynamic mechanic analysis (DMA) and thermogravimetric analysis (TGA).