In this study, olive husk flour was added to poly(lactic acid) (PLA) to produce fully biosourced and biodegradable composites. In particular, untreated and alkali treated particles were used to produce the biocomposites at 20 wt.% via melt extrusion followed by injection moulding. The samples were then subjected to accelerated ageing (UV irradiation and water spray at 50°C) for different amounts of time (120, 240, 360 and 480 h). The results show that accelerated ageing decreased the tensile strength (TS) and Young's modulus (YM) for both untreated and alkali treated biocomposites, but the treated particles presented a lower reduction. Further comparison was made via differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) to detect any changes in the samples.