The influence of the pressure in the ethanol/water pulping of sugarcane bagasse was studied using argon pressure varying from 0.5 to 1.5 MPa. The reaction volume and activation volume were studied. For the reaction volume, temperature and time were constant and pressure was varied, and for the activation volume, temperature was constant and pressure and time were varied. The degradation of cellulose was not promoted by the pressure with positive reaction volume (4100 cm(3)/mol). On the other hand, degradation of xylan (polyoses) and lignin was strongly favored by the pressure and reaction volume ranged from -1000 to -3000 cm(3)/Mol.