Cellulose nanocrystals were extracted from Agave angustifolia fibres by alkali and bleaching treatments followed by acid hydrolysis. The chemical composition of the Agave fibres was determined at different stages of chemical treatment. The structural analysis was carried out by a Fourier Transform Infrared spectroscopy and X-ray diffraction. The morphology and thermal stability of the Agave fibres at different stages of chemical treatment were investigated by field emission scanning electron microscopy and thermogravimetric analysis, respectively. The results indicated that the hemicellulose and lignin were removed extensively from the extracted cellulose. The two peaks at 1735 cm-1 and 1247 cm-1, which were attributed to the C=O stretching and C-O out of plane stretching vibration of the hemicellulose and lignin in raw Agave, completely disappeared in the spectra of chemically treated fibres. The X-ray diffraction data showed enrichment in the portion of crystalline cellulose from 59% to 82% in the raw and cellulose nanocrystals, respectively. Thermogravimetric analysis showed that the thermal stability improved significantly by various chemical stages. The size reduction of the Agave cellulose into nano-sized particles from 7 µm to 8 nm in diameter by acid hydrolysis was confirmed with transmission electron microscopy images.