Abstract: The interlaminar fracture behavior of two high modulus carbon/epoxy composites (HM/4211 and HM/TDE86) has been investigated in mode Ⅰ,mode Ⅱ and mixed mode.The double contilever beam (DCB) test,the end notched flexure (ENF) test and the mixed mode bending (MMB) test were conducted to determine the interlaminar fracture toughness and the failure locus in mixed mode for the two composites.The data and results obtained from this investigation are useful for material selection and quality assurance in space structure application,and furthermore,for establishing design allowable used in damage tolerance analyses of composite structures made of these materials.