This study aims to find out an equation of state for Krypton gas (Kr) in the temperature range 120–130 K and to calculate some of its thermodynamic properties. The virial equation of state for Krypton gas (Kr) is constructed using the quantum second virial coefficient (Bq). The Beth–Uhlenbeck formula is used to calculate the quantum second virial coefficient Bq in the temperature range 120–130 K at different number densities. The pressure-volume-temperature behavior of Kr gas is carefully investigated, from which the phase (gas-liquid) transition is predicted. Some of the thermodynamic properties; the internal energy, enthalpy, and Helmholtz free energy are calculated for a number density of 4×1025 atoms/m3 using the quantum second virial coefficient. Our results show that the deviation from ideality becomes most significant at low temperatures and increases with increasing number density. Our results for the quantum second virial coefficient are in good agreement with previous results.