The dynamic process of underpotential deposition (UPD) of copper on iodine-modified Pt(111) electrode in sulfuric acid solution was investigated by in situ scanning tunneling microscopy and ex situ low-energy electron diffraction. Prior to the copper deposition, iodine adlayer structures were characterized by both techniques. II was found that well-ordered iodine adlayers with the structures of (3 x 3) and (root 7 x root 7)R19.1 degrees could he prepared by immersion of the electrode in a solution containing iodide ions under potential control, It was also found that the interconversion of the two structures was very slow. After the UPD of copper on the iodine-modified Pt electrode, the iodine atoms formed a c(p x root 3R-30 degrees) structure with a p value of ca, 2.6 on the (1 x 1) copper adlayer on Pt(lll). After the copper was stripped, the electrode exhibited a mixture of (3 x 3) and (root 7 x root 7)R19.1 degrees structures of iodine on Pt(111).