Monatomic steps with a height of 0.25 nm on ultraflat Au(111) surfaces during electrochemical dissolution can be seen for the first time by a laser confocal microscope combined with a differential interference contrast microscope (LCM-DIM). Atomic force microscopy images were acquired in the same area in order to confirm that the step lines observed by LCM-DIM are mostly monatomic steps with the height of 0.25 nm. Successively recorded LCM-DIM images indicated that the anodic dissolution of Au(111) takes place only at step edges in solutions containing chloride anions at potentials near the onset of anodic current.