Highly purified cellulose was separated from wheat straw by sequential treatments of dewaxed straw with 0.5-M aqueous KOH at 35degreesC for 2.5 h under ultrasonic irradiation time of 0 to 35 min, 2% H2O2-0.2% TAED at pH 11.8 for 12 h at 48degreesC, and with 80% acetic acid-70% nitric acid (10/1, v/v) at 120degreesC for 15 min. The yield of crude cellulose preparations obtained by first two-stage treatments ranged between 45.3% and 46.9% of the dry weight straw which contained 7.3 to 7.9% residual hemicelluloses and 3.3 to 3.7% residual lignin, and had molecular weights ranging from 269,960 and 258,280 g mol(-1) determined by their viscosity, while the purified cellulose samples separated by a further treatment of the corresponding crude cellulose with 80% acetic acid-70% nitric acid, are relatively free of bound lignin (0.1 to 0.2%) and contained minor amounts of associated hemicelluloses (similar to3%), but gave much lower molecular weights ranging between 42,300 and 44,650 g mol(-1) estimated by GPC in DMAc/LiCl system indicating that the final step treatment with 80% acetic acid-70% nitric acid resulted in a noticeable degradation of the cellulose except for removal of residual hemicelluloses and lignin. However, there was no evidence of increased acid or aldehyde by oxidation in all the purified cellulosic preparations. Both crude and purified cellulose samples were characterized by FT-IR and CP/MAS C-13-NMR spectroscopy. The thermal stability of the purified cellulosic preparation was higher than that of the crude cellulosic sample.