Abstract The properties of fracture toughness (mode-II) of nanostitched carbon/epoxy composites were investigated. The mode-II of the nanostitched structure demonstrated extraordinary enhancement considering to the control sample. It was proved that carbon nanostitching yarn in the though-the-thickness of the preform structure was adequate. The fundamental mechanism for raising the mode-II strength in the nanostitched composite was the interlayer matrix breakages predominantly as a form of shear hackle marks in where nanostitching suppressed the layer to layer opening in stitching region during crack growth. Multiwall carbon nanotubes in the matrix and filament also diminished the stress clustering perhaps as a form of friction, filaments/matrix debonding in the interlaced unit cell and filament slippage in the failed matrix zone. So, nanostitched carbon/epoxy composite showed better interlainar shear properties.