In this paper the failure behaviour of composite materials in the skin-stiffener of wind turbine blade structures are investigated. In order to achieve this, the laminated composite beams were stitched using glass, carbon and Kevlar yarns before curing process. Four different moulds of T-beam with adhesive; T-beam with stitches; Box-beam with adhesive and Box-beam with stitches were studied in this work. These specimens were tested under quasi-static loading condition to compare the failure resistance of adhesive and stitched bonding methods. Experimental results indicated that stitching can significantly improve failure load and interlaminar fracture resistance of the joints in wind turbine composite blade structures. The cohesive zone modelling (CZM) technique which is known as a variation in the cohesive stresses with the interfacial opening displacement along the localised fracture process zone is also used to predict bonding failure in the skin-stiffener of wind turbine blade structures. (C) 2015 Elsevier Ltd. All rights reserved.