Abstract: A technique was developed for simultaneous ESR-electrochemical measurements of surface radicals on porous electrodes. The ESR-electroehemical cell consists of a Teflon bonded carbon electrode(WE) and a porous Ag electrode(CE)packed parallelly with a separator in between. A grain of Ag/Ag_2O is placed in the separator,serving as the reference electrode. The electrolyte contained in the cell is no more than 4μl, confining the dielectrical loss to an tolerable level. Using the cell we have been able to obtain the ESR signals of surface radicals generated by electroreduction for a quinone-modified RB carbon electrode. To our best knowledge, this is the first report on ESR spectra with hfs for species adsorbed on electrode surfaces. It is deduced from the ESR data that on the electrode surface there are several absorbed radicals with different electrochemical behaviors. In the potantial range studied, there seem to be four types of surface quinoid compounds which can be reduced according to a radical mechanism. Two of them exhibiting hfs are probably surface species linked to the carbon surface by a singl bond, (possibly through a surface group) while the other two which give the anisotropic spectra are assumed to be multi-site absorbed.