Ionic liquids (ILs), an alternative to conventional molecular organic solvents, have attracted the attention of the scientific community because of their tunable unique physicochemical properties. Among the tested strategies, addition of co-solvents is the most convenient choice to alter the physicochemical properties of ILs for their industrial applications. In the present article, we have measured the density (rho), speeds of sound (u), and refractive index (n(D)) for six binary mixtures of N-methylaniline (NMA) and N-ethylaniline (NEA) + BmimBF(4)+ HmimBF(4)+ OmimBF(4) over the entire range of composition and at temperatures ranging from 293.15 to 323.15 K at 5 K intervals and at atmospheric pressure. Excess molar volume (V-m(E)), excess molar isentropic compressibility (K-s,m(E)), and deviation in the refractive index (Delta(phi)n(D)) on volume fraction basis were calculated from these measured thermophysical properties. Influence of temperature on the excess and deviation properties has been studied. V-m(E),K-s,K-m,(E), and Delta(phi)n(D) were fitted to the Redlich-Kister polynomial equation, and the parameters for the binary coefficients are reported. The influence of the alkyl chain length of ILs on the thermophysical properties of the mixtures of secondary amines was studied. We have discussed the intermolecular interactions between the ILs and amine molecules using well-known arguments. We further predicted the refractive indices of the studied mixtures using various mixing rules, and the resulting values have been compared with the experimental values through the standard deviation. Experimentally calculated excess molar volumes have been compared with the predicted values of the Prigogine-Flory-Patterson theory and the extended real association model at 298.15 K.