Film thickness changes occurring at substrates immersed in solutions can be measured by scanning electrochemical microscopy (SECM). The measurement is based on the SECM feedback method in which the tip-substrate separation is determined. Two different approaches, with or without a mediator, were employed to demonstrate the applicability of SECM for these measurements with selected model systems (AgBr on Ag; Cu deposition; TiO2 formation on Ti). The measurement resolution of this technique was 10 nm to 1 mu m depending on the size of the tip electrode. The advantages and disadvantages of this technique and the factors affecting resolution are discussed.