The high interface sensitivity in the ellipsometric phase shift, Delta, makes total internal reflection ellipsometry (TIRE) a useful tool to study redox reactions on the electrode surface. Electrochemistry - total internal reflection ellipsometry (EC-TIRE) is proposed to observe the refractive index change induced by the reduction of the dissolved oxygen (DO) on Clark electrode. In order to analyze the TIRE signal change caused by the reaction, we have calculated the refractive index variation on the surface of Clark electrode. We have found that the calculation under the thin layer boundary condition is more persuasive than that under the semi-infinite boundary condition not only in the steady state measurement but in the dynamic process. (C) 2014 Elsevier Ltd. All rights reserved.