Density and dynamic viscosity data of binary mixtures of ionic liquids (ILs) were determined in this work, at temperatures from 283.15 to 363.15 K and at 0.1 MPa. The mixtures of two ILs comprise a common cation and different anions, combining 1-butyl-3-methylimidazolium bis-(trifluoromethylsulfonyl)imide with eight other ionic liquids, namely, 1-butyl-3-methylimidazolium thiocyanate, 1-butyl-3-methylimidazolium dicyanamide, 1-butyl-3-methylimidazolium tricyanomethane, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium acetate, 1-butyl-3-methylimidazolium trifluoromethanesulfonate, and 1-butyl-3-methylimidazolium dimethylphosphate. Five mole fractions (0.00, 0.25, 0.50, 0.75, 1.00) of each mixture were prepared and characterized in terms of density and dynamic viscosity. The temperature dependence of density was described using a linear model, while the Vogel-Tammann-Fulcher equation was used to describe the temperature dependence of viscosity. Ideal mixing rules were used to predict the molar volume and viscosity and to infer on the mixtures ideal/nonideal behavior. For the mixtures of ILs investigated almost null or small deviations were observed in the molar volumes, meaning that their mixing is remarkably close to linear ideal behavior when molar volumes of mixtures are considered. For viscosity, larger deviations were observed for some particular systems; yet, and in general, mixtures of ILs do not deviate in a significant extent from ideal behavior. Therefore, ideal mixture models can be used to predict the physical properties of mixtures of ILs and to a priori design mixtures with specific features.