Abstract: The objective of this paper is mainly to study the fracture toughness of 3240 Glass-Weave/Epoxy and[O2/±45/±45/O2]s Graphite/Epoxy laminated composites by using theory and techniques of anisotropic linear elastic fracture mechanics. In order to determine the fracture toughness of the two laminates three different techniques including K-Calibration, J-Integral and Energy methods are utilized. Anisotropic factors in K-Calibration formula and J-Integral equation are calculated by the use of authors' SI-FJTAP finite element program capable of handling eight-node isoparametric elements and their collapse modes. The equation J = 2U （ 1+1/2（W -a）/（W + a））/（B（W-a））is applied in Energy method. Experiments for compact tension specimens over a range of ratios of crack length to specimen width, a/W, and different pre-notched directions （a） to one of the laminate's principal axes are conducted on INSTRON 1251 material testing machine. The critical load is determined based on the load versus notch opening displacement （P- ） curves.Experimental results show that the anisotropic theory of linear elastic fracture mechanics can be used to study the fracture behavior of laminated composites prior to initiation. The fracture toughness of the two kinds of laminates are found to be constant for varying ratio a/w but strongly dependent on the principal moduli of the laminates and on the angle a. Both parameters, KQ and JQ, characterizing fracture resistance of composite laminates are equivalent and good agreement exists among the three distinct approaches.