The in-plane shear properties of nanostitched three-dimensional (3D) carbon/epoxy composites were investigated. Adding the stitching fiber or multiwalled carbon nanotubes or nanostitched fiber into carbon fabric preform slightly improved the shear strength and modulus of stitched and stitched nanocomposites. The in-plane shear fracture of the base and nanostructures was extensive delamination and tensile fiber failures in the sheared region. But, the stitched and stitched nanocomposites had angular deformation of the stitching yarns in the fiber scissoring areas, shear hackles in the matrix and successive fiber breakages in the interlayers. Probably, this mechanism prohibited extensive interlayer opening in the nanostitched composites. The results exhibited that introducing the stitching fiber (1.44%) and multiwalled carbon nanotubes (0.03125%) in the base structure enhanced its transverse fracture properties as a form of confined delamination area. Therefore, the damaged tolerance properties of the stitched nanocomposites were enhanced.