The electrochemical behaviors of iridium electrodeposited in 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid were studied. Cyclic voltammograms prepared on the gold electrode suggested that Ir(III) was reduced to iridium with an irreversible one-step process, which was controlled by the diffusion of Ir(III). The diffusion rate is 3.83×10_?11 m₂/s and the average transfer coefficient is 0.083. The morphology and composition of iridium coatings prepared on molybdenum substrates were characterized by scanning electron microscopy, X-ray diffraction and X-ray photoelectron spectroscopy, respectively. The morphology of iridium coatings was dependent on the potential, time and current density of electrodeposition. Compact coatings were obtained at the reduction peak potential with a balance between the nucleation rate and the growth rate. Flat and compact coatings were formed when current density ranged from 0.5 to 1.82 mA/cm₂ in the galvanostatic electrodeposition.