This article reports the influence of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl) imide (BMITFSI) addition on the thermal and mechanical properties of regenerated cellulose. Scanning electron microscopy, Young's modulus values, thermogravimetric analysis, glass-transition temperature values, and ultraviolet-visible spectroscopy were used to assess the effect of BMITFSI addition on the properties of regenerated cellulose. The addition of a room-temperature ionic liquid, BMITFSI, during the dissolution of cellulose was found to enhance the thermal stability of regenerated cellulose. Compared to other reported plasticizers for regenerated cellulose, such as glycerol, glycols, water, mineral oil, and alpha-monoglycerides, the low vapor pressure of BMITFSI led to a long performance with the least evaporation or leaching. In addition, the immiscible nature of BMITFSI in water and its stability against moisture made BMITFSI an effective plasticizer for regenerated cellulose over a broad range of surrounding humidities and temperature conditions. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121: 750755, 2011