A continuous anodic electrolysis of an iridium oxide-tantalum oxide (70:30 mol%) coated titanium electrode in a 4 mol dm(-3) NaOH solution were carried out to assess the electrode's durability. The electrode's potential during the electrolysis indicated that the potential was almost constant except at the end of electrolysis, which could be easily known with a drastic increase in potential. The electrode's lifetime under the same operation conditions was linearly dependent of the amount of the oxide coating. The compositional and morphological changes in the oxide coating during the electrolysis were studied by XRF and SEM. Both iridium oxide and tantalum oxide were rapidly consumed immediately after the electrolysis started, and then the consumption rates became small. The consumption of tantalum oxide was larger than that of iridium oxide so that the mole ratio of iridium oxide became higher than the initial value. The coating surface enriched with iridium oxide was also suggested by SEM observation. From the results obtained, the electrode was proven to have a high stability in such a concentrated alkaline solution comparable to that in an acidic solution.