Physical properties of hydrogen isotopes, hydrogen (H2), hydrogen-deuterium (HD), hydrogen-tritium (HT), deuterium (D2), deuterium-tritium (DT), and tritium (T2) were estimated through vapor pressure prediction, and validated by steady-state simulation of ITER isotope separation system (ISS). Peng–Robinson (PR) equation of state with Twu alpha function was selected for modelling which showed favorable prediction from the experimental vapor pressures of each hydrogen isotopes. The steady-state simulation of ITER ISS using Aspen Plus consists of four distillation columns and seven equilibrium reactors with four purified products: D2, T2, HD, and DT. Converged solution from simulation produced potential scenario for actual ITER ISS process.