Agave Americana (agave) and Agave sisalana (sisal) fibres belong to the same family of natural fibres. Both the fibres were treated with alkali. Interestingly, alkali-treated agave fibres displayed a clean and smooth surface, whereas alkali-treated sisal fibres showed a rough surface due to the rupture of alkali-sensitive bonds. This indicated that the sisal fibres are more susceptible to alkali treatment as compared to agave fibres. The experimental studies of chemical composition, Fourier transform infrared spectroscopy and X-ray diffraction were also carried out. Both alkali-treated agave and sisal fibres were used to reinforce polyfurfuryl alcohol (PFA) matrix. The effect of these fibres on the mechanical and thermo-mechanical properties of PFA composites was examined. Mechanical, thermal and thermo-mechanical properties of the composites were studied. The results indicated the improvement in mechanical and thermal properties of the reinforced PFA.