The critical liquefaction of rice straw to bio-oil with sub- and supercritical mixtures (ethanol-water and 2-propanol-water mixture) was studied in a 1000 ml autoclave at 533-623 K, 6-18 MPa, respectively. The results showed that the maximum yield of bio-oil was 39.7% for the 2-propanol:water volume ratio of 5:5 at 573 K, while the higher heating value (HHV) of bio-oil increased with the reaction temperature and solvent volume ratio. The formation of low-boiling-point materials was reduced by a mixture. Using a Mixture could inhibit the formation of residue and then promote the conversion of rice straw with the ratio of 1:9-5:5. The bio-oil was analyzed by GC/MS and Elemental Analyzer, while the morphological changes of residue were observed by a scanning electron microscope (SEM). (C) 2007 Elsevier Ltd. All rights reserved.