Ternary IrO2-SnO2-Sb2O5 is among the best electrocatalysts for O-2 evolution. Its compositions, especially its Ir content, have significant impacts on the electrochemical stability, activity, and cost of the electrode. In this paper, the effects of Ir content on the electrochemical stability and activity of the Ti/IrO2-SnO2-Sb2O5 electrodes were investigated. Experimental results show that the electrochemical stability initially increased with nominal Ir content until 10 mol%. From 10-30 mol%, the effect of Ir composition gives insignificant difference. Further increase in Ir content beyond 30 mol% resulted in a decrease in the electrochemical stability. The performance of the electrode depends on all the steps it was made with about 15 % variation observed at Ir content of 20 mol%, where the longest average accelerated service life was found to be 1063 h under the conditions of anodic current density of 10 000 A/m(2) in 3 mol/L H2SO4 electrolyte at 70 degrees C. The study on electrode degradation and failure mechanism reveals that the development of cracks or pores in the coating surface, the loss of Sb and Ir contents, and crystalline structure change of the coating during the life test facilitated the deactivation of the electrode. Moreover, the non-conductive TiO2 interlayer formation was found to be responsible for the peeling of the coating layer, leading to the failure of Ti/IrO2-SnO2-Sb2O5, especially with high Ir content (> 30 mol% in nominal).