This study evaluated the effects of sodium hydroxide (NaOH) treatment on the nutritional value of Arundo donax (A. donax). Its ultimate goal was to develop an environmentally friendly animal feed alternative that could be produced sustainably while combatting the spread of A. donax. Plants were collected and dried at 60 °C in an oven with controlled air circulation to determine the dry matter (DM) content. The dry plant material was then sprinkled with an NaOH solution of 2%, 4%, 6%, or 8% and placed in leak-proof containers for four weeks. The chemical and in vitro digestibility properties of treated and untreated A. donax samples were analysed in triplicate. The treatment led to significant decreases in neutral detergent fibre (NDF) from 81.06% DM to 69.39% DM, acid detergent fibre (ADF) from 46.99% DM to 43.19% DM, and ether extract (EE) from 2.06% DM to 1.39% DM, in the untreated samples compared with those treated with 8% NaOH, respectively. In addition, DM digestibility increased from 24.61% to 33.78%, ash content from 11.75% DM to 19.92% DM, and ADL from 7.43% M to 15.38% DM. Thus, treatment of A. donax with an 8% solution of NaOH concentration improved its nutritional value.