This work presents an assessment of the damage mechanisms occurring during tensile tests in hybrid flax-glass fibres reinforced epoxy composites. The samples were composed of twill flax and glass fibre laminate plies with different stacking sequences and subjected to water immersion at 55 °C. The Acoustic Emission (AE) technique combined with scanning electron microscopy observations was used to identify the typical damage mechanisms and to follow their evolution. This identification was made with a statistical multivariable analysis in which the number of parameters and classes was optimised. Finally, the participation of each damage mechanism to the global failure was evaluated from the hits number and AE energy. The AE results showed that, although the hits number associated with the fibre failure was the lowest, their contribution to the overall failure of composites became predominant regarding the cumulative of AE energy. Furthermore, an additional group of AE signals induced by the delamination between flax and glass fibre layers was detected for the aged hybrid laminates.