Ionic liquids (ILs) can act as high-performance solvents for cellulose in biomass conversion processes. However, the increase in viscosity that occurs upon dissolution of the cellulose in ILs can cause problems. To overcome this problem, ILs can be mixed with an organic solvent. This study investigates the thermal risk of the cellulose dissolution process using mixed solvents, ILs, and organic solvents. Sealed-cell differential scanning calorimetry (SC-DSC) was conducted on mixtures of 1-butyl-3-methylimidazolium acetate (BmimAc) and three aprotic polar solvents [dimethyl sulfoxide (DMSO), dimethyl acetamide (DMAc), and N,N-dimethylformamide (DMF)] to investigate thermal hazards. In addition, for samples exhibiting exothermal behavior greater than 100 J g(-1), a prediction of runaway reaction behavior was obtained using kinetic analysis. Results revealed that BmimAc/DMSO could undergo a violent exothermic reaction, with a risk of a runaway reaction depending on the process temperature.