Very smooth thin films of iridium have been deposited on super polished fused silica (SiO2) substrates using dc magnetron sputtering in argon plasma. The influence of deposition process parameters on film micro roughness has been investigated. In addition, film optical constants have been determined using variable angle spectroscopic ellipsometery, over the spectra range from vacuum ultraviolet to middle infrared (140 nm-35 ?m). Also the surface roughnesses were measured by atomic force microscopy (AFM).