Ozone is usually generated from oxygen gas using a silent discharge apparatus and its concentration is less then 10 mol%. Ozone is condensed by the adsorption method, which is widely used for the growth of oxidation thin films such as superconductor. Highly condensed ozone is analyzed by three methods; ultraviolet absorption, thermal decomposition and Q-mass analyzing methods. Thermal decomposition method is most effective in the highly condensed ozone region and its method is superior to Q-mass analyzer for determining ozone concentration because of the simplicity of the method. The decomposition. of condensed ozone takes place mainly on the inner surface of the vessel. Ozone concentration decreased to less then 50 mol% over a 8 h period. (C) 2003 Elsevier Science B.V. All rights reserved.