Density, speed of sound, and refractive index for the binary mixture (1,4-dioxane (1) + isobutyric acid (2)) were measured over the whole composition range at temperatures T = (295.15, 298.15, 301.15, 304.15, 307.15, 310.15, and 313.15) K and at the atmospheric pressure. From the experimental data, excess molar volume V-E, excess isentropic compressibility kappa(E)(S), excess speed of sound c(E), excess refractive index n(E), molar refraction R, and deviation in molar refraction Delta R were calculated. These results have been fitted to the Redlich-Kister polynomial equation. The excess molar volume, excess isentropic compressibility, and deviation in molar refraction were found to be negative, whereas excess speed of sound and excess refractive index were found to be positive for all temperatures. The thermodynamic properties have been discussed in terms of nature of molecular interactions between the components of the mixture.