The surface morphology and electrocatalysis of IrO2-based anodes prepared by thermal decomposition are investigated by SEM observation and polarization measurements for oxygen evolution. The surface structure of the IrO2-Ta2O5 catalytic layer on a titanium substrate varies with the preparation procedures, pretreatment of the substrate and coating method. The coating surface essentially consists of cracks, flat areas, and IrO2 particles formed both on the flat areas and in the cracks. Fine IrO2 particles with sizes of 30-100 nm are confirmed on the flat area of the coating, which is prepared on a smooth surface of a titanium substrate by a dipping method. Roughening the substrate surface makes the coatings heterogeneous with an increase in the number of cracks and induces the growth of the IrO2 particles. Tafel plots obtained using IrO2-Ta2O5 anodes having different coating surface morphologies are also presented. The results suggest that the catalytic activity of the coating for oxygen evolution is significantly influenced by the number of fine IrO2 particles rather than by the heterogeneity of the coating surface.