Thermal gravimetric analysis (TGA) has been used to determine the kinetics of decomposition for 1-butyl-2,3-dimethylimidazolium tetrafluoroborate ([BMMIM][BF4]) and to identify the effects of contaminants on the decomposition temperatures. Data were collected from both isothermal and constant ramp rate programs for the decomposition of [BMMIM][BF4] under N-2. The isothermal data were fit to a global kinetic model and the apparent Arrhenius parameters were determined. The constant heating rate data were used to determine the apparent activation energy using the isoconversional method developed by Friedman. The effects of up to 10 wt.% water, NH4BF4, NH4Cl, and [BMMIM][Cl] impurities on [BMMIM][BF4] decomposition temperatures were investigated. The only contaminant to significantly affect the decomposition was NH4Cl, resulting in some decomposition at the temperatures associated with [BMMIM][Cl] decomposition. Published by Elsevier Ltd.