The interlaminar fracture toughness properties based on the double cantilever beam test of the multilayered stitched carbon/epoxy/multiwall carbon nanotube prepreg woven composites was investigated. The fracture toughness based on beam theory and modified beam theory of the stitched/nano and stitched composites showed 3-fold and 2-fold increases compared to the base and base/nano composites, respectively. The fracture toughness resistance to arrest the crack propagation in the stitched/nano composite was primarily due to out-of-plane directional stitching fiber bridging and was secondarily due to in-plane directional biaxial fiber bridging and multiwall carbon nanotubes. Fracture surfaces of the stitched/nano had multiple matrix and brittle tensile filament breakages in carbon stitching yarn and ductile filament breakages in the para-aramid stitching yarns where filament/matrix debonding and filament pull-out were identified. (C) 2017 Elsevier Ltd. All rights reserved.