6th European Workshop on Structural Health Monitoring. Dresden. Germany. 2012. Report. In recent years high interests of scientific and industrial worlds were concentrated on natural fibers composites. Natural fibers as hemp, flax and sisal have become suitable alternatives to glass fibers as NFs present several advantages as lightness, strength, recyclability and are relatively cheap and abundant. However, their high hygroscopic nature and their sensitivity to temperature must be taken into account. In this paper, the influence of hygrothermal aging on mechanical behaviour of Hemp/ isotactic polypropylene composites were studied using flexural tests associated to acoustic emission (AE).