Ionic liquids(ILs) have been expected to be promising alternative to traditional solvent in the industrial processing and derivation of cellulose, due to their unique property such as low vapor pressure, high chemical stability and good solubility[1-3].This work presents the gamma radiation effect on the microcrystalline cellulose (MCC) dissolved in 1-butyl-3-methylimidazolium chloride([Bmim]Cl) ILs.The radiation-induced changes in average molecular weight (Mη) and degradation kinetics of MCC in [Bmim]Cl were investigated using viscometric method(Fig.1).The radiation-induced degradation rate (k) was calculated and compared with that using N-methylmorpholine-N-oxide (NMMO) as the cellulose solvent.Moreover, the effect of co-solvent—DMSO on the k was investigated.Finally, the possible radiation degradation mechanism of MCC in the [Bmim]Cl was discussed.This work provides a useful and feasible method to control the molecular weight of cellulose without derivation.