In order to improve the high-temperature service property of Ir, a well-bonded single-layer pure IrAl intermetallic coating was prepared on Ir by pack cementation followed by vacuum annealing treatment. The oxidation behavior of the IrAl coating was investigated by cyclic oxidation tests at 1400–2000 °C and compared with that of pure Ir. The results showed that the IrAl coating, although containing many cracks, exhibited excellent oxidation resistance over the whole experimental temperature range. The reasons were deduced to be the in situ formation of Al2O3 and the sintering of the cracks in the IrAl layer. The excellent oxidation protective effect of the single-layer IrAl coating can be ascribed to its stable and unique as-oxidized microstructure, i.e., double-layer structure of Al2O3/Ir′, which showed excellent compatibility and comprehensive property.