Recently, a method was presented for the dissolution and nuclear magnetic resonance analysis of cell wall components in lignocellulosic biomass, which involves cell wall ball-milling, dissolution in ionic liquids (ILs), in situ acetylation, and the recovery of acetylated materials. However, the dissolution in ILs and the relatively long ball-milling times may partially degrade the plant cell wall components. In the present study, the molecular weight (MW) distributions of acetylated biomasses from fir ( Abies sachalinensis ), birch ( Betula platyphylla ), and bamboo ( Phyllostachys nigra ) recovered from IL systems were examined by size exclusion chromatography. The effects of IL types, cosolvents, dissolution temperatures and times, and ball-milling times were evaluated. The MW of acetylated fir woods recovered from 1-allyl-3-methylimidazolium chloride at 30–80°C or from 1-butyl-3-methylimidazolium chloride at 100°C for 2 h were similar to those materials that were recovered from the N -methylimidazole/dimethyl sulfoxide system. In contrast, a significant decrease in MW was observed with 1-ethyl-3-methylimidazolium acetate ([Emim]OAc) even at 30°C. The degradation of cell wall components in [Emim]OAc was reduced to some extent in the presence of N , N -dimethylacetamide or pyridine. The MW decreased gradually with increased ball-milling time.