Hydrogen adsorbed on Ru/ZrO2 was studied by FT-IR (Fourier transform infrared) spectroscopy. While the Ru-H (Ru-D) species was not observed, the H2O (D2O)-like species was formed by H-2 (D-2) introduction on ZrO2. The H2O (D2O)-like species was characterized by a band at around 1600 (1190) cm(-1) due to the bending mode and by a broad band at 2500-3800 (2000-2700) cm(-1) attributed to the stretching mode. The H2O (D2O)-like species was stable under evacuation at 300 K, but desorbed as H-2 (D-2) at 370 K. The H2O (D2O)-like species was considered to be produced by spillover of hydrogen (deuterium) atoms dissociatively adsorbed on Ru particles to react with the surface lattice oxygen atoms of ZrO2. The heat of formation and the activation energy of the H2O (D2O)-like species formation from H-2 (D-2) were 134 +/- 11 (172 +/- 11) kJ mol(-1) and 28.6 +/- 3.2 (36.6 +/- 5.6) kJ mol(-1), respectively. The difference between the H2O-like species and adsorbed H2O molecules on Ru/ZrO2 was also examined.