Choline acetate, a totally bio-derived ionic liquid (IL), was used for IL-assisted pretreatment and subsequent fractionation of bagasse into carbohydrate and lignin. The fractionated carbohydrate-rich material (CRM) and lignin-rich material (LRM) were 79.6% and 5.2% of the original bagasse, respectively. CRM contained nearly all carbohydrate and approximately 50% of lignin in the original bagasse. In addition, approximately 20% of lignin in the original bagasse was fractionated as LRM. The cellulose saccharification percentage was over 95% for CRM, although the value was only 20% for the original bagasse. The average molecular weight of LRM was 4.2 x 10(4), which was approximately ten-times lower than that of the hydrolysis residue of CRM. After five cycles of the processes, the recovery of choline acetate was 80% of the fresh one. Throughout the five cycles, choline acetate maintained its chemical structure and exhibited its pretreatment capability for fractionation and enzymatic hydrolysis of bagasse. (C) 2014 Elsevier B.V. All rights reserved.