A thermosetting epoxy polymer was hybrid-modified by incorporating 9 wt.% of CTBN rubber microparticles and 10 wt.% of silica nanoparticles. The resin was poured into steel mould and cured to produce bulk epoxy polymer sheets from which fatigue test specimens were machined. The total fatigue life of the hybrid-modified epoxy polymer was determined by conducting constant amplitude fatigue tests with dog-bone shaped test specimens, at a stress ratio, R = σ min/σ max = 0.1, using a sinusoidal waveform at a frequency of 3 Hz. Further, the fatigue crack growth behavior of the hybrid-modified epoxy polymer, at a stress ratio, R = 0.1, was determined using a standard 50 mm wide compact tension specimen. The fatigue fracture surfaces were observed using a scanning electron microscope. The cyclic fracture toughness of the hybrid-modified epoxy polymer, estimated from the fracture surface analysis, correlated well with the reported values of the toughness; which was significantly greater than that of the neat epoxy polymer. The energy dissipating micromechanisms of, (i) rubber particle cavitation and plastic deformation of the surrounding material, and (ii) silica nanoparticle debonding followed by plastic void growth, were observed to be operative, resulting in an improved fracture toughness. The fatigue crack initiation and propagation lives were determined from the experimental data. The enhanced capability to withstand longer crack lengths, due to the improved toughness together with the retarded crack growth rate, were observed to enhance the total fatigue life of the hybrid-modified epoxy polymer. © 2012 World Scientific Publishing Company.