The plane-strain fracture toughnesses of two different particle-filled epoxies have been measured using compact tension specimens. Significant increases in toughness were observed (up to about 50 with 30% volume fraction of bead). In the phenolic bead-filled epoxy, the major toughening mechanism is crack pinning, while in the carbon bead-filled epoxy, localized plastic deformation associated with particle-matrix debonding and transparticle fracture lead to the toughening. The interlaminar fracture behaviors of hybrid composites, based on bead-filled epoxy matrices, have been investigated using DCB (double cantilever beam) and ENF (end notch flexure) specimens for Mode I and Mode II tests, respectively. The hybrid composite based on carbon bead shows an increase in both GIc initiation and GIIc values as compared to a GFRP laminate with unmodified epoxy matrix. The optimum bead volume fraction for the hybrid composite is about 15% by volume of the matrix. However, the unmodified epoxy glass fiber composite shows a higher GIc propagation value than that of the hybrid composites due to fiber bridging, which is less pronounced in the hybrids, as the presence of the beads results in a matrix-rich interply region. The relationship between the Mode I interlaminar fracture mechanics parameters (i.e., GIc and KIc values), obtained from DCB specimens, has been reviewed using orthotropic fracture mechanics.