Dissolution and crystalline structure changes of cellulose treated by 1-butyl-3-methylimidazolium chloride [C4mim]Cl-water mixtures were investigated at 90℃ under 1.0 MPa. Amorphous cellulose was found to be partial dissolved in the [C4mim]Cl-water mixtures with [C4mim]Cl content of 60%—95%

and adding deionized (DI) water into the cellulose-[C4mim]Cl solution for cellulose regeneration. The crystallinity index (CrI) and the dimension of average crystallite size (Dhkl) for MCC obviously change with increasing treatment duration

but retain the characteristic shapes of cellulose I crystalline structure. There are significant oscillations in the intensities of hydrogen bonds of cellulose for the mixtures with different [C4mim]Cl content. Different contents of ionic liquid have different effect on microcrystalline cellulose.