The electrochemical detection of dissolved ozone in water was examined using boron-doped diamond (BDD) electrodes. A well-defined reduction peak was observed at ∼380 mV for H-terminated BDD, whereas it was observed at ∼200 mV in the case of O-terminated BDD for an ozone solution in a 0.1 M phosphate buffer solution at pH 7. The peak potential for ozone reduction was selective with respect to oxygen reduction at both H- and O-terminated BDD electrodes, whereas it occurred at approximately the same potential as oxygen reduction at other types of solid electrodes, including glassy-carbon, platinum, and gold electrodes. Interference from chlorine was not observed in lower concentration than 300 μM ClO-. Furthermore, in order to apply the detection technique to electrolyte-free media, BDD microelectrodes were also used. A linear calibration curve for dissolved ozone in water could be achieved between concentrations of 0.49 and 740 μM, with an estimated detection limit (S/N = 3) of 0.185 μM (S/N = 3). Excellent stability was demonstrated for repetitions of these calibration curves performed in 3 consecutive days.