The dispersion of nanoparticles plays a key role in enhancing the mechanical performance of polymer nanocomposites. In this work, one hybrid epoxy nanocomposite reinforced by a well dispersed, zinc oxide functionalized, multi-wall carbon nanotube (ZnO-MWCNT) and core-shell rubber (CSR) was prepared, which possesses both high modulus and fracture toughness while maintaining relatively high glass transition temperature (T_g). The improved fracture toughness from 0.82 ​MPa ​m^1/2 for neat epoxy to 1.46 ​MPa ​m^1/2 for the ternary epoxy nanocomposites is resulted from a series of synergistic toughening mechanisms, including cavitation of CSR-induced matrix shear banding, along with the fracture of MWCNTs and crack deflection. The implication of the present study for the preparation of high-performance polymer nanocomposites is discussed.