This paper aims at investigating the effect of alkali treatment and water ageing on several short Alfa fibre reinforced polypropylene composites. For this purpose, different composites with untreated and treated fibres were elaborated by extrusion and injection moulding processes and subjected to water ageing. The obtained results showed that the alkali treatment enhances significantly the Young’s modulus and tensile strength of the Alfa fibre reinforced polypropylene composites and reduces their loss during water ageing. The acoustic emission analysis showed that the use of alkali treatment plays a major role in the improvement of the fibre-matrix interface of both unaged and aged composites. [ABSTRACT FROM AUTHOR]