Alkali-treated straw and cellulose xanthorgenate were derived from shoot and root biomass of Eichhornia crassipes by treatment with NaOH and CS(2), respectively. The structures of the raw and modified plant materials were characterized by XRD, TGA/DTA, and FTIR. Alkali treatment increased the crystallinity of raw plant material, while the subsequent CS(2) treatment had the reverse effect. The thermal stability of the plant material was diminished by alkali treatment but was restored by subsequent CS(2) treatment. Alkali treatment removed most of the lignin and hemicellulose from the raw plant material, whereas the formation of cellulose xanthogenate introduced new C=S and O-CS-S functional groups. (C) 2009 Published by Elsevier Ltd.