Excess molar isobaric heat capacity, density and speed of sound of a cyclohexanone and benzene mixture were measured at 298.15 and 308.15 K. From densities, excess volumes were calculated at two temperatures and the excess expansion factor of the mixture was estimated. The excess expansion factor was negative and large, and affected the estimation of isothermal compressibility and isochoric heat capacity from density, speed of sound, isobaric heat capacity and expansion factor.