This work presents density and dynamic viscosity data for the pure ionic liquid, 1-butyl-2,3-dimethylimidazolium tetrafluoroborate, [Bmmim] [BF4], and its binary mixtures with the highly polar solvents dimethylsulfoxide (DMSO) and acetonitrile (ACN), over the entire range of composition and temperatures from (298.15 to 353.15) K at atmospheric pressure. The properties have been represented with temperature by specific equations, both for pure [Bmmim][BF4] and its binary mixtures. Therefore, an empirical linear equation was used for density variation and for viscosity, the Vogel-Fucher-Tammann (VET) equation. From the density data the excess molar volume, V-E, apparent molar volume, V-phi nu and partial molar volume, (V) over bar (m nu) as well as thermal expansion coefficient, alpha(p), have been evaluated. Moreover, the excess molar volume was fitted to the Redlich-Kister polynomial equation, and its variation with composition has been qualitatively discussed in terms of interaction and structural factors.