The critical liquefaction of rice straw in sub- and supercritical 1,4-dioxane-water mixture was investigated in a 500 mL autoclave at temperature of 260-340 degrees C, resistance time of 0-20 min, and volume ratios 0-100 vol.% (1,4-dioxane: mixture). The yields of oil and PA + A (preasphaltene and asphaltene) were in the range of 29.64-57.30 wt.% and 6.42-22.68 wt.%, depending on the temperature, resistance time and volume ratio. The synergistic capability of 1.4-dioxane-water mixture could allow the great decomposition of the tubular structure of lignocelluloses. It was shown by the results that the "oxygen-transfer" reaction, deoxygenation and decarboxylation may occur in the liquefaction of rice straw with 1,4-dioxane-water mixture, while deoxygenation and decarboxylation may be the main reaction. The oil and PA + A fractions obtained at different volume ratios were analyzed by FTIR and GC-MS to investigate the effect of the ratios on the type of the compounds in the liquid products. It is shown that the nucleophilic and hydrolytic functions of water might be weaken at the higher ratio of 1,4-dioxane runs, resulting the lower amount of phenolic, acidic, hydrocarbon and ester derivatives in the oil and PA + A fractions. (C) 2008 Elsevier B.V. All rights reserved.