The present paper describes work carried out to compare the strength performance of PLA reinforced aligned discontinuous harakeke and hemp fibre mat composites evaluated experimentally and using various simple elastic mathematical prediction models. Fibre mats were produced by means of Dynamic Sheet Former (DSF), and stacked alternately with PLA sheets to produce composites with up to 40 wt% fibre content. The fibre content was increased from 5 wt% to 40 wt% using 5 wt% interval. In this work, both harakeke and hemp composites were manufactured using hot-press. It was found that, better agreement to the experiment was obtained for Young’s modulus compared to those composite strengths. The Modified Rule of Mixtures is found to give accuracy within 41% for strength, while the Cox model showing the best agreement (<10%) for Young’s modulus for fibre contents up to 25 wt%. Better agreement obtained for Young’s modulus is believed to due to less mechanism involved at where Young’s modulus is measured.