The layer of nickel hydroxide was formed electrochemically on the reduced surface of polycrystalline Ni in 1 M KOH. The layer thickness of 8.5 nm, estimated by an electrochemical method, corresponded to about 10 monolayers of Ni(OH)(2). In situ atomic force microscopy (AFM) with the tip fixed was applied to monitor the changes of nickel hydroxide film thickness during the process of its oxidation and reduction. The process of oxidation resulted in the film thickness decreasing by about 3 nm. This change could be explained as due to the removal of a proton from the Ni(OH)(2) layer.