Pretreatment is the key to unlock the recalcitrance of lignocellulosic biomass for the productions of biofuels. Ionic liquid pretreatment has drawn increased attention because of its numerous advantages over conventional methods. In this study, corncob was submitted to pretreatments with 1-ethyl-3-methylimadazolium acetate (EMIMAc) and/or H(2)O/dimethyl sulfoxide (DMSO) followed by alkaline extraction to isolate hemicelluloses. The hemicellulosic fractions obtained were comprehensively characterized with a series of chemical and spectroscopic technologies, including gel permeation chromatography (GPC), thermogravimetric analysis (TGA), high-performance anion-exchange chromatography (HPAEC), Fourier transform infrared (FTIR) spectroscopy, and one- and two-dimensional nuclear magnetic resonance (NMR). The results showed that the fractions prepared with ionic liquid pretreatments exhibited relatively higher average molecular weights (196,230-349,480 g/mol) than the fraction prepared without pretreatment (M(w), 96,260 g/mol). Furthermore, the pretreated fractions demonstrated higher thermal stability compared to the fractions without pretreatment. Structural characterization indicated that all of the fractions had similar structures, which are composed of a (1 → 4)-linked β-D-xylopyranosyl backbone substituted with arabinofuranosyls attached to O-2 and O-3 and with 4-O-methyl-α-D-glucuronic acid also linked to O-2.