The reaction rates of ozone with free cyanide species were determined by a stopped-flow spectrophotometer in the pH range 2.5-12.0. The direct reaction of molecular ozone and the free radical reactions which contribute to the overall reaction were identified. A reaction mechanism consistent with the observations was proposed. The rate constant for the direct reaction of molecular ozone with cyanide ion was calculated to be 2600 +/- 700 M/sup -1/ s/sup -1/. Batch and bubble-column experiments indicated stoichiometric conversion of cyanide to cyanate and an ozone consumption of 1.2 +/- 0.2 mol/mol of oxidized cyanide.