Abstract: A series of nanostructured films exhibiting high surface roughness were prepared by using square wave oxidation-reduction cycles (SWORC) on Pt microelectrodes. Scanning tunneling microscope (STM) studies illustrated that all the films were made up of Pt islands. Measurement showed that along with the increase of average thickness of nanostructured films from 58 to 139 nm, the average dimension of Pt islands in the film increased solely from 102 to 114 nm, and the average height of Pt islands varied from 15 to 18 nm.Employing CO adsorption as molecule-probe reaction, IR properties of the prepared nanostructured Pt films of different roughness were investigated by using in situ FTIR spectroscopy. The results revealed that CO linearly adsorbed (COL) on all nanostructured Pt films prepared in this paper yielded Fano-like spectra, i.e., the IR absorption of COL on nanostructured Pt film gave rise to a bipolar IR band (asymmetric line shape), which may be attributed primarily to the size effect of Pt islands.