This paper describes the influence of hygrothermal ageing on mechanical properties and damage behaviour of quasi-unidirectional flax-fibre reinforced epoxy (FFRE) composite. The evolution of water absorption for FFRE composite appears to be Fickian and the kinetics parameters are influenced by the temperature variation. Young’s modulus and tensile strength are clearly affected by the hygrothermal ageing because a significant reduction in Young’s modulus is shown while tensile strength decreases much less for water-saturated composites. The decrease of both properties could be explained by a reorientation of flax microfibrils and the plasticiser effect of water on the matrix, which are both stimulated by moisture absorption. Acoustic emissions analysis combined with scanning electron microscopy enabled investigating the effects of hygrothermal ageing on the process of degradation of flax-fibre composite.