The vapour pressure differences between a mixture of (propane + cyclopropane) and cyclopropane and between propane and cyclopropane have been measured simultaneously with the absolute vapour pressure of cyclopropane. This was done at 13 temperatures between 175 K and 210 K, as a function of composition. The mixtures show small positive deviations from Raoult’s law. The excess molar Gibbs energy (G(m)(E)) has been calculated from the vapour pressure data and fitted to the equation G(m)(E)/(RTx(1)x(2) = (-0.2490 +/- 0.0072) + (81.8 +/- 1.4)/T. The estimated value of the excess molar enthalpy (H-m(E)) for the equimolar composition, in the same temperature range is 170 +/- 4 J mol(-1). The results were interpreted using Deiters’ equation of state.