Abstract. In the present research, 1,3-dimethyl-imidazolium dimethyl phosphate ([Mmim][DMP]) ionic liquid was applied to dissolve alkali lignin from wheat grass to prepare for lignin micro/nano-particles. The alkali lignin can be dissolved completely at 80°C in 30 min under microwave condition with [Mmim][DMP] (solid-liquid ratio of 1:10) which is easy to be recycled. The dissolved lignin can be precipitated by diluting the ionic liquid-lignin solution with water to get lignin micro/nano-particles with diameter ranged from 200 nm to 1.5 μm. Structural analyses with Gel permeation chromatography (GPC), 2D heteronuclear single quantum coherence nuclear magnetic resonance (2D-NMR), Thermogravimetric Analysis (TGA), etc., indicate that a large number of dehydration reactions occurred during dissolution process to result in the generation of unsaturated bonds with higher degree of unsaturation (Ω) (from 197-334), lower polydispersity (from 1.49 to 1.12) and lower average molecular weight (from 8634 to 5406 Da). Compared with original alkali lignin, the regenerated alkali lignin as micro/nano-particles showed higher thermal stability. It was also found from the 2D NMR spectra that the cleavages of aryl-ether bonds dramatically happened during the dissolution process, [Mmim][DMP] ionic liquid is more likely to destroy lignin units linked by β-O-4′ bonds to G-type lignin with less steric hindrance, resulting in the least amount of β-O-4′ linkages. In addition, dehydration and demethylation of lignin occurred during the dissolution of ionic liquid.