Adding toughening particles to composite laminates is a common approach to increase their delamination resistance. More recently, interleaving the laminated structures with electrospun (thermoplastic) nanofibrous veils is shown to be a viable toughening method. Where toughening composite laminates with nanofibrous interleaves becomes more and more evident under static conditions, the effectiveness under fatigue loadings has yet to be proven. This article provides insight in the nanofibre toughening mechanisms acting under fatigue conditions. Several nanofibre types with a high potential for toughening are considered. A substantial decrease of the delamination propagation rate up to one order of magnitude was obtained for all tested nanofibre types. Furthermore, two distinct zones of delamination behaviour are observed in nanofibre interleaved laminates on exposure to cyclic loading. These insights reveal the crucial design parameters which allow for the production of nanofibre toughened composites with an improved fatigue life. (C) 2016 Elsevier Ltd. All rights reserved.