Crack growth behavior and toughening mechanism of epoxide resin filled with varying volume fraction of phenolic bead has been stuided using compact tension specimens. In particular the effect of volume fraction on the fracture toughness values($K_IC$) and major toughening mechanism was investigated. It has been shown that the crack propagation behavior can be explained principally in terms of crack pinning and volume fraction effect upon $K_IC$ values. $K_IC$ values tend to increase with increasing volume fraction. Comparison of experimental results with predicted values using crack pinning theory and modeling showed that predicted values are higher than the measured values. These results can be explained by the difference between the crack pinning modeling and real material condition such as bonding(between bead and epoxy) condition.
