The trialkyl-substituted imidazolium-based ionic liquids (ILs) are considered to be promising as supporting electrolytes for electroplating and other electrochemical applications because of their increased stability compared to that of dialkyl-substituted compounds. Basic properties like density, viscosity, and conductivity of 1-butyl-2,3-dimethylimidazolium tetrafluoroborate (BMMImBF(4)), 1-butyl-2,3-dimethylimidazolium azide (BMMImN(3)), and their mixtures were measured. The thermal stability of the azide IL permits its use up to 423.15 K, whereas the upper temperature limit for telrafluoroborate IL extends to 623.15 K. The electrochemical stability with regard to cathodic reduction was the same for both ILs; the decomposition potential was about -1.9 V versus the Ag/AgCl reference electrode. However, the resistance to electrochemical oxidation at the anode was much lower for the azide IL. The decomposition potential was 0.5 V against 2.05 V for the tetrafluoroborate IL.