Tin oxide (SnO2) thin film was micromachined by the electrochemical reduction process in various electrolyte solutions. The electrode gap, current density, and kind of electrolyte solutions for electrochemical reduction of tin oxide film were optimized. Very high resolution was achieved in neutral or basic solutions, when the electrode gap was 0.1 mm and a large current density such as 5 A/cm(2) was applied for very short time, 1 s. High current density and very short reaction time avoided the deposition of reduced species of tin oxide on the machined area, resulting in the high resolution. Moreover, photolithographical pattern etching of five parallel straight lines with the widths 0.02-0.1 mm was performed and very high resolution was obtained when the substrate was patterned and the Pt plate was used as counter electrode.