Comprehensive high-performance epoxy nanocomposites were successfully prepared by co-incorporating organo-montmorillonite (o-MMT) and nano-SiO2 into epoxy matrix. Because of the strong interaction between nanoscale particles, the MMT layers were highly exfoliated, and the exfoliated nanoscale MMT monoplatelets took an interlacing arrangement with the nano-SiO2 particles in the epoxy matrix, as evidenced by X-ray diffraction measurement and transmission electron microscopy inspection. Mechanical tests and thermal analyses showed that the resulting epoxy/o-MMT/nano-SiO2 nanocomposites improved substantially over pure epoxy and epoxy/o-MMT nanocomposites in tensile modulus, tensile strength, flexural modulus, flexural strength, notch impact strength, glass transition temperature, and thermal decomposition temperature. This study suggests that co-incorporating two properly selected nanoscale particles into polymer is one pathway to success in preparing comprehensive high-performance polymer nanocomposites. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 3503-3510, 2012