Hydrogen isotope exchange reactions occurring in (H2O, D-2) or (D2O, H-2) reacting system under a Dc electrical discharge were investigated using spectroscopic methods such as Fourier-transform infrared (FTIR) and plasma emission spectroscopy (PES). The progress of the reactions was determined by real-time measurement of the the IR absorbance of HDO molecule, a major product of the reaction. The progress of the reaction was studied as a function of the temperature, the current density, and the composition of the reactants, while the pressure of the system was maintained at approximately 67 mbar. The results revealed that the discharge method was far more effective in facilating the exchange reaction than was the conventional catalytic method. The (H2O, D-2) System also generated a significant amount of D2O besides HDO and HD as the ratio of D-2 to H2O was increased The transient species of the system, such as H or D atoms, were monitored during the discharge using emission spectroscopy. The analysis of the final products by mass spectroscopy confirmed that neither H-2 nor O-2 was among the major products of the system in the discharge.