Supported iridium catalysts were prepared using the method of incipient wetness by impregnating various supports with a solution of iridium trichloride. The behaviors of hydrogen adsorption on the reduced catalysts were investigated by means of TEM, measurements of the adsorption isotherm in the temperature range of 273 similar to 473 K, calculation of the isosteric heat and the activation energy. The maximum capacity of hydrogen adsorption on the supported iridium catalysts appeared at the mid-temperature at 323 K instead of 273 K. This abnormal phenomenon suggested that an activated process was necessary during hydrogen adsorption on the supported iridium catalysts. The energy barrier of this activated process was calculated to be 31 similar to 34 kJ mol(-1). Furthermore, two types of adsorbed hydrogen with distinct isosteric heat ( -65 similar to -40 kJmol(-1) and -20 kJmol(-1)) were found through analysis of the hydrogen adsorption isotherms using the Clausius-Clapeyron equation. These two types of adsorbed hydrogen were believed to derive from hydrogen adsorption on the subsurface layer and surface layer of the iridium crystallites, respectively.