Dissolved ozone up to 34 mg/L was generated by direct electrolysis of water using a titanium electrode coated with an antimonydoped tin dioxide film. The electrode was prepared by spray pyrolysis at 520 degreesC. The current efficiency of ozone generation was 15% in a 0.1 M HClO4 aqueous solution at room temperature. The electrolytic generation of ozone depends critically on the composition and morphology of the coating and a good generation was observed with Sb: Sn atomic ratio of 1: 7 and a smooth and compact surface with connected particles of 3-5 nm diameter. (C) 2004 The Electrochemical Society.