Growth behavior of iridium (Ir) thin film on Si substrates prepared by plasma enhanced atomic layer deposition (PEALD) was systematically studied. Ir(EtCp)(COD) and oxygen was employed as a precursor and reactant, respectively. To obtain optimal conditions for depositing nanometer scale Ir thin film, deposition temperature, cycle dependence and precursor feeding time dependence were studied. Uniform 12 nm thick Ir layer with sharp interface was grown at the temperature range of 330-360 degrees C at the fixed deposition cycles of 300. The grown Ir film showed linear properties as a function of deposition cycles which is a typical self-limiting characteristic of ALD. The XRD patterns revealed that IrOx was not formed due to relatively low partial pressure of oxygen. The optimal conditions obtained for 12 nm thick Ir thin film were 330 degrees C of deposition temperature, 300 deposition cycles, and 10 sec of precursor feeding time.