The objective of this study was to characterize the performance of untreated and chemically treated harakeke fibre (a leaf fibre from a plant native to New Zealand) and compare with hemp fibre to assess its use as potential reinforcement in composites. Alkali treatment is among the most popular treatments used to remove unwanted fibre constituents such as pectin, hemicellulose and waxes; it can enhance fibre properties, fibre separation, interfacial bonding and fibre dispersion within a composite. Physical and mechanical properties of untreated and alkali treated fibres were assessed using single fibre tensile testing, X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal analysis using thermogravimetric analysis (TGA). Untreated harakeke fibre was found to be lower in tensile strength compared to untreated hemp fibre. It was also found that the tensile strength of harakeke and hemp fibres treated with 5wt% NaOH/2wt% Na2SO3 and 5wt% NaOH was not significantly affected and these fibres had good fibre separation. However, alkali treatment was found to lead to higher crystallinity index (Ic) and better thermal stability for harakeke as well as hemp fibres.