© The Author(s) 2014 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav. This paper is a novel application of acoustic emission (AE) technique to investigate the actual occurring modes of delamination damage (i.e. mode I, mode II and the combination of these pure modes) in glass/epoxy composites. AE parameters and mechanical information associated with some novel methodologies were used to develop new AE-based approaches for studying delamination damage. The inter-laminar fracture energy for the initiation of delamination, Gc, was also measured using the novel introduced methods and standard methodologies. The results indicate that different interface lay-ups and different GII/GT modal ratio values indicate different AE signals and mechanical behaviors. Scanning electron microscope was also used to observe the induced damage mechanisms. It was found that the presented methods of employing AEs to characterize delamination damage and to obtain Gc were successful, especially in mode II and mixed-mode conditions where unstable crack growth and difficult crack growth monitoring prohibit a rigorous measurement of Gc. The results of this study could lead to improve automatic techniques for health monitoring of the real composite structures.