In this work, silica-filled epoxy composites were prepared for use as substrate materials in electronic packaging applications. The effects of silica content on cure behaviors and rheological properties of epoxy/silica composites were studied. Differential scanning calorimetry (DSC) results indicate that the main exothermic peaks of the composites moved to high temperatures with increasing silica content. The gelation time of the composites increased with the addition of silica. The rheological behavior of the composites changed from liquid-like to solid-like behavior with increasing silica content, which was due to the strongly aggregated clusters of silica particles Keywords: Epoxy resin, Silica, Composites, Cure behaviors, Rheological properties