Insituelectrochemical scanning tunneling microscopy (STM) was applied to single‐crystal platinum(111), rhodium(111), and palladium(111) surfaces in an aqueous sulfuric acid solution. Atomically flat surfaces of Pt(111) are roughened in solutions by the electrochemical oxidation–reduction cycle. It is shown that a single potential cycle causes the formation of many adatoms and very small clusters on the Pt(111) terrace. A steady‐state surface structure can be clearly observed after applying a few potential cycles. The STM image is composed of regularly arrayed islands whose diameter and height are in the ranges of 2–3 and 0.5–0.75 nm, respectively. Atomically flat terrace‐step structures can be also observed on Rh(111) and Pd(111) surfaces. The effect of oxidation–reduction cycle on these surfaces is also discussed.