Abstract The cellulose-dissolving ability and some physical properties of mixed solvents of an amino acid IL, N-methyl-N-(2-methoxyethyl)pyrolidin-1-ium 2,6-diaminohexanoate ([P1ME][Lys]), with polar aprotic solvents, such as 1,3-dimethylimidazolidinone (DMI), N,N-dimethylformamide (DMF), dimethylsulfoxide (DMSO), and acetonitrile (CH₃CN), have been investigated. The viscosity was significantly reduced by the increasing content of polar aprotic solvents, and a 1:1 mixture (molar ratio) of [P1ME][Lys] with DMF showed 91.5 cP which corresponded to less than 1/10 compared to that of the pure IL at 25 °C (1058 cP). The β values of the mixed solvents, which have the IL contents over 0.1, exhibited β-values similar to that of the pure IL. On the other hand, the π-value was dependent on the ratio of the IL content, and the pure IL had the highest π-value. We found that the mixed solvent of [P1ME][Lys] with DMF (1:1) easily dissolved the cellulose and the mixed solvent could be used to extract cellulose from moso bamboo (Phylostachys heterocycla) powder. The efficiency of the extraction of cellulose from the bamboo powder was significantly increased when a 1:1 mixture of the IL with a polar aprotic solvent was used as the extracting solvent at 60 °C; the extraction ratio of the 1:1 mixture (IL: DMF) reached twice that of the pure IL. We thus obtained cellulose in 18% (w/w) yield from the bamboo powder.