Natural fibre reinforced composites arouse a growing interest in many applications due to their low carbon footprint and their interesting mechanical performance. In some sectors, fire specifications are also required and lead to the use of flame retardant additives. Due to the hydrophilic nature of the reinforcement, biocomposites are sensitive to humid ageing [1]. Therefore the question arises: what is the influence of flame retardants on ageing behavior and the final fire performance of these materials? In this study, flax fibre reinforced epoxy composites flame retarded by Aluminium diethyl phosphinate or DOPO were submitted to ageing in different humid atmospheres or by immersion in liquid water. Water sorption kinetics of FR biocomposites were studied and discussed with regard to Fick absorption model [2]. Their fire properties were also studied using cone calorimeter. The influence of ageing is only noticeable at high water content. The effect on the HRR curve depends on the nature of FR and is mainly governed by the way water molecules are absorbed into the materials.