The adsorption of H₂ and D₂ at various temperatures and the isotope effect have been studied in detail over a ZrO₂ catalyst by means of FTIR. Four different types of adsorbed hydrogen were observed as follows: (1) molecularly adsorbed hydrogen, H₂(a), was observed below 173 K and was easily desorbed by evacuation; (2) homolytic dissociative adsorption produces Zr[graphic omitted] species was observed below 373 K and was stable below 178 K; (3) heterolytic dissociative adsorption which forms OH and ZrH was observed in the temperature range 223–373 K and the isotope effect of adsorption between H₂ and D₂ was also found; (4) the adsorption which generates two OH bands at 3778 and 3668 cm^–1 takes place above room temperature. For the heterolytic dissociative adsorption of H₂ and D₂, both the kinetic and the equilibrium isotope effects were observed. The magnitude of these isotope effects is in good agreement with the values calculated via IR data.