Abstract Probabilistic edge-delamination strength of a thermosetting polymer composite was studied experimentally in this work. During the procedure, by means of edge-delamination tensile test, the graphite–fiber/epoxy laminate made of unidirectional Toray P7051S-20Q-1000 prepregs with an optimized lay-up of [122/–122/02]S was used for examining its probabilistic distributions of the edge-delamination onset stress and the ultimate tensile strength. Acoustic emission (AE) equipment and optical microscope were utilized to capture the edge-delamination initiation and characterize the failure modes during delaminating. Fractographical analysis based on scanning electron microscope (SEM) was conducted for the characterization of the microscopic failure mechanisms of the composite laminate during edge delaminating. Probabilistic models were introduced for data reduction. Test results show that the edge-delamination onset stress and the ultimate tensile strength of the laminate tested satisfy two two-parameter Weibull distributions very well. AE signals show the main failure mode during edge delaminating is interlaminar shear failure, corresponding to that predicted by numerical simulation and confirmed by SEM fractographical results in this study.