The toughness mechanism of the liquid crystalline epoxy resin DGE(C2-MS-C2))-which has an alpha-methylstilbene moiety as a mesogenic group and ethylene oxy units as spacers-cured with diaminodiphenylethane (DDEt) was investigated using time-resolved wide-angle X-ray diffraction (WAXD) measurements performed during tensile tests. The WAXD patterns of the isotropic (ISO) and LC networks of DGE(C2-MS-C2)/DDEt indicated the molecular chains in the networks were oriented along the elongation direction, with the LC network being more highly orientated than the ISO network. The dissipation energy generated during the reorientation of the network chains was proposed as the origin of the high fracture toughness of DGE(C2-MS-C2)/DDEt.