The concept of intermittent interlaminar bonding is investigated as a means of improving the fracture toughness of cross-ply Gr/Ep composites without significant loss of tensile strength and modulus. The concept of linear elastic fracture mechanics(LEFM)is used to study the effects of strong bonded area and bonding composites. The experimental results indicate that the fracture toughness and notch strength of intermittent interlaminar bonded composities are improved and the tensile strength only decreased by 3-8% in comparison to those of the fully bonded composites. Damage zones around the crack tip are detected by the modified X-Ray non-destructive testing technique and the fractography. The improvement of toughness is explained based on the damage zones. The mechanisms of damage zone are shown to be caused by subcrack along the fiber on the 0.deg. ply, matrix cracking along the fiber on the 90.deg. ply, interlaminar delamination, and ply pull-out of the 0.deg. ply.