Abstract: Micro IrO₂-pH electrodes were prepared under three heat treatment conditions:700℃ furnace cooling, 870℃ air cooling and 870℃ furnace cooling. Their linear response range and response time were compared. The results indicate that heat treatment conditions have significant effect on the uniformity of iridium oxide films and the open potential stability and response time of the electrodes. After both 700℃ furnace cooling and 870℃ air cooling, the oxide films have rough surfaces, non-uniform porosities and crevices; whereas after 870℃ furnace cooling, the oxide films appear with improved characteristics, such as a more uniformity, a shorter response time and a better linearity of open potential. It is concluded that during iridium oxidation, iridium is oxidized by O₂ in air with high temperature Li₂CO₃ as a solvent. The H⁺ response is caused by the reaction of hydrous iridium oxide on the electrode and H⁺ ions in the solution, resulting in the transition of Ir⁴⁺ and Ir³⁺.