Feedstock particle size can influence the lignocellulosic conversion yields and the energy costs of second generation ethanol production. In this work the influence of bagasse particle size on pretreatment and enzymatic hydrolysis was evaluated. Bagasse was ground using a knife mill equipped with screens to obtain particles of 0.5, 1.0 and 2.0 mm (sieve opening). Unmilled and milled samples were pretreated using dilute sulfuric acid in different conditions of temperature and time. The pretreated bagasses were subject to enzymatic hydrolysis for 72 hours. The pretreatment yield was determined from the mass loss during pretreatment for each assay and sample. The chemical compositions of untreated and pretreated bagasse were used to evaluate hemicellulose solubilization in pretreatment; and hydrolysis conversion was measured to assess the effect of particle size enzymatic saccharification. The higher mass loss and hemicellulose solubilization (39 and 87 %, respectively) occurred for the more severe conditions of pretreatment, 140 degrees C for 30 min. However, there was no statistically significant difference (p=0.05) of mass loss for the samples with different particle sizes. In enzymatic hydrolysis, the higher percentage of hydrolyzed mass was also for the pretreatment at 140 degrees C for 30 min (58-60), which was obtained >90 % of the sugars conversion. There was no significant difference (p=0.05) for hydrolyzed mass of samples with different particle sizes Ver menos