Nine cholinium ionic liquids (ILs) were synthesized. A high solubility of lignin (up to 483 mg g(-1)) and xylan (up to 721 mg g(-1)) was observed in four ILs containing organic anions, while cellulose, chitosan, and keratin were scarcely soluble in all ILs. These ILs were used for wheat straw pretreatment. Among the nine ILs tested, cholinium taurate ([Ch] [Tau]) was the best. The effects of biomass particle sizes, water contents, and biomass loadings on the IL pretreatment were studied. Readily digestible residues were obtained after wheat straw up to 2 mm size was pretreated. Additionally, this IL pretreatment process was highly tolerant toward moisture. A good reducing sugar yield (79.7%) was achieved in the enzymatic hydrolysis of wheat straw pretreated by [Ch] [Tau] at a biomass loading of 10% under 80 degrees C for 6 h. Therefore, renewable sulfonate-based cholinium ILs may be promising solvents for pretreatment and fractionation of lignocelluloses.