Electrical double-layer properties of variously treated Bi(001) and Bi(111) electrodes were studied in terms of the Debye length dependent roughness theory (i.e., nonlinear Poisson-Boltzmann theory), recently developed by Daikhin et al. The geometrical roughness factor, root mean square (rms) departure of the surface from flatness, the medium lateral correlation length values have been obtained. According to the experimental data and results of theoretical calculations, the surface roughness increases in the order of Bi electrodes: electrochemically polished single-crystal Bi(111) plane, cut at the temperature of liquid nitrogen Bi(111) plane, electrochemically etched Bi(111) plane, chemically etched Bi(111) plane, chemically etched Bi(001) plane. This order of the electrode surface roughness is in agreement with the ex situ AFM data, i.e., with the rms roughness R-ms values. At small electrolyte concentrations (c(el) less than or equal to 0.01 M), the deviation of experimental roughness function vs. inverse Debye length curves from the theoretically calculated ones has been observed, which is explained by the influence of energetic inhomogeneity of the polycrystalline surfaces, i.e., the nonequal surface charge density values at the various homogeneous regions exposed at the macropolycrystalline electrode surface, on the interfacial capacitance values. (C) 2003 The Electrochemical Society.