Two novel ionic liquids, benzylmethylammonium propionate and benzylmethylammonium hexanoate, were synthesized and the densities (ρ) speeds of sound (u) and viscosities (η) of their mixtures with N,N-dimethylformamide (DMF) in the concentration range of 0.067–0.573 mol·kg−1 were measured at 293.15–328.15 K. The relative viscosity (η r) and viscosity B-coefficients were calculated from measured viscosity data. Apparent molar volumes, V ϕ , and compressibilities, K s,ϕ have been calculated from experimental density and speed of sound data and the corresponding values at infinite dilution are estimated by the Redlich–Mayer equation. The results have been interpreted in terms of interaction of the ionic liquids with the organic solvent. The calculated apparent molar volume at infinite dilution (V ϕ ∞) values indicate that ionic liquid–molecular solvent interactions are stronger for benzylmethylammonium hexanoate in DMF than the benzylmethylammonium propionate in DMF mixtures. The limiting apparent molar expansibilities, E ϕ ∞, at each temperature for both binary solutions have positive values and increase with increasing temperature.