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 (G(m)(E)) and the excess molar volume (V-m(E)) are positive. For the equimolar mixture G(m)(E) = 118.8 J.mol(-1) at 161.40 K, G(m)(F) = 91.7 J.mol(-1) at 182.34 K and V-m(F) = 0.248 cm(3).mol(-1) at 182.34 K. The estimated value of the excess molar enthalpy (H-m(E)) 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.