Intense electrochemiluminescence (ECL) was observed from sandwich cells. The cell structure is as follows: F-doped SnO2/nanoporous TiO2/tris (2,2'-bipyridyl) ruthenium (II) complex [Ru(bpy)(3)(PF6)(2)] in acetonitrile/ F-doped SnO2. Intense ECL was observed only when negative cell voltage was applied to nanoporous TiO2 electrodes. The ECL increased with an increase in the surface area of porous TiO2 layers. ECL increase was observed for porous ZnO electrodes, but not for porous SnO2 electrodes. It was concluded that increases in ECL are associated with the formation of Ru+ in porous TiO2 electrodes and the process taking place after reduction of Ru2+ which occurs in the porous electrodes. (c) 2005 The Electrochemical Society. [DOI: 10.1149/1.1946587] All rights reserved.