The mode-II interlaminar fracture toughness properties following the end notched flexure method of nanostitched carbon/epoxy nanoprepreg composites were studied. The fracture toughness (G(IIC)) of the nanostitched and stitched composites showed 3.4 fold and 2.7 fold increase compared to the control, respectively. Thus, the nanostitching improved the mode-II toughness of all the carbon/epoxy composites with regard to the nano, and base composites. It was assumed that the type of stitch fiber as well as fabric pattern, in particular prepreg carbon stitching fiber and satin prepreg woven fabric, was effective. The basic mechanism for the enhancement of the G(IIC) toughness in the nanostitched composite was the interlaminar resin layer failure especially as a form of shear hackle marks where nanostitching arrested the delamination in the stitching zone during crack propagations. Multiwall carbon nanotubes in the matrix and filament also mitigated the stress concentration probably as an outline of debonding/pull-out/stick-slip/friction. Therefore, nanostitched as well as stitched carbon/epoxy woven composites exhibited improved damage tolerance performance with regard to the base composites.