The influence of the hydrothermal treatment conditions of rice straw (temperature - 150-190 degrees C, time - 0-20 min after reaching the operation temperature - and liquid/solid ratio - 6-8), on the composition of liquid and solid fractions wassStudied. Polynomial models were found for to reproduce the experimental results with errors less than 6%. Operating to 190 degrees C, 15 min and 9 liquid/solid ratio was obtained high values of glucose (1.92 g/L), xylose (3.97 g/L), arabinose (0.99 g/L) and acetic acid (1.96 g/L), what allows to save capital when not operating with the maximum time and/or liquid/solid ratio; yield in the solid fraction is 88.1% and lignin content 24.43%. If what it is required to obtain good values of yield (96.46%) and lignin content, is necessary to operate to 150 degrees C, obtaining lower concentrations glucose (1.11%). xylose (2.78%), arabinose (0.56%) and acetic acid (0.39%). Ethanolamine pulping of solid fraction of hydrothermal treatment provides pulp with higher or similar properties to those obtained of pulping rice straw with ethanolamine or soda. (C) 2009 Elsevier Ltd. All rights reserved.