The electrochemical STM method has been applied to a hydrotalcite clay-modified electrode with the aim of obtaining evidence for the formation of a surface layer of the [Fe(CN)(6)](3 -/4-) couple. As a result, ordered surface layers of [Fe(CN)(6)](3 -/4-) ions on a hydrotalcite-modified electrode have been observed with an in-situ electrochemical STM instrument: the initial lattice of [Fe(CN)(6)](3-) with a = 1.40 +/- 0.03 nm, b = 1.85 +/- 0.04 nm and alpha = 63 +/- 3 degrees changed to an expanded lattice of [Fe(CN)(6)](4-) with a = 1.94 +/- 0.04 nm, b = 1.90 +/- 0.04 nm and alpha = 60 +/- 3 degrees due to the electrochemical reduction.