To improve the enzymatic digestibility of sweet sorghum bagasse and bioethanol production, five pretreatment methods have been investigated and compared, including (1) dilute NaOH solution autoclaving pretreatment, (2) high concentration NaOH solution immersing pretreatment, (3) dilute NaOH solution autoclaving and H2O2 immersing pretreatment, (4) alkaline peroxide pretreatment and (5) autoclaving pretreatment. Among them, the best result was obtained when sweet sorghum bagasse was dilute NaOH solution autoclaving and H2O2 immersing pretreatment. The highest cellulose hydrolysis yield, total sugar yield and ethanol concentration were 74.29%, 90.94 g sugar/100 g dry matter and 6.12 g/L, respectively, which were 5.88, 9.54 and 19.13 times higher than the control. Moreover, the FIR and SEM analysis illustrated significant molecule and surface structure changes of the sweet sorghum bagasse after pretreatments. (C) 2012 Elsevier Ltd. All rights reserved.