The total vapor pressure of liquid mixtures of xenon and diborane has been measured at 161.40 K (the triple point of xenon) and at 182.34 K (the triple point of dinitrogen oxide), as a function of composition. The liquid densities were also measured at 182.34 K. The mixtures show positive deviations from Raoult's law. Both the excess molar Gibbs energy ( ) and the excess molar volume ( ) are positive. For the equimolar mixture = 118.8 J.mol-1 at 161.40 K, = 91.7 J.mol-1 at 182.34 K and = 0.248 cm3.mol-1 at 182.34 K. The estimated value of the excess molar enthalpy ( ) was found to be 328 J.mol-1. The results were interpreted using the Deiters equation of state. This is the first thermodynamic study of the xenon + diborane system.