To evaluate the interlaminar fracture behavior of composite materials subjected to combined state of stresses, a modified ENF specimen is proposed and analyzed. The ratio of Mode I and Mode II energy release rate ($G_I/G_{II}$) can be controlled by changing the thickness ratio of end notch. Modified ENF specimens with various thickness ratios and crack lengths are tested in order to determine critical loads at the initiation of interlaminar crack. Test results are used for the evaluation of total energy release rate($G_c$) and used as input data in the current analysis. For the analysis of test specimens, a finite element method (FEM) and conventional beam theory are utilized. In the FEM analysis, singular elements are introduced in front of crack tip and a formulation is applied for separating each component of $G_I$ and $G_{II}$. The FEM solution shows a good agreement with the beam theory solution. It is found that the modified ENF specimen is very efficient to evaluate mixed mode interlaminar fracture toughness.
