The effect of microstructure on the mechanical properties of 2D PAN fiber reinforced mesophase pitch-based carbon/carbon (C/C) composites was studied by polarized light microscope (PLM), scanning electron microscope (SEM), transmission electron microscope (TEM) and mechanical properties test techniques respectively. PLM results indicate that the structure of the mesophase pitch matrix is graphitic and anisotropic. TEM and SEM results show the mesophase pitch matrix is the lamellae layer structure and the fiber-matrix interface morphology is similar to the "fissured-type 〞interface. The non-brittle fracture behavior of the composites is related to multiple crack deflections caused by the fiber-matrix interface and delamination microcracking within the pitch carbon layers. The fractured surfaces are made of fracture and pulling out of fiber. The flexural strength and the fracture toughness (K_IC) of C/C composites are 257MPa and 11.4MPa·m ^1/2, respectively.