Electrochemical oxidation of histidine (His) at an anodic oxidized boron-doped diamond electrode (AOBDDE) was performed. A significant peak of His oxidation is observed at about +1.5 V vs. Ag/AgCl, however, the response current was inhibited due to strong His-oxidized product adsorption onto the electrode surface. The characteristics of the His-oxidized product adsorbed onto the electrode surface were investigated by studying the electrochemical behavior of the Fe(CN)(6)(4-) redox reaction using cycle voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Both CV and EIS results showed a decrease in the sum of transfer coefficients and an increase in the electron transfer resistance, which indicate that the adsorption film is a non-conductive film. The most possible active site locations for the AOBDDE for His oxidation are within these low-lying polycrystallite AOBDDE surface regions. The results from Raman and X-ray photoelectron spectroscopy offer strong evidence of the imidazole ring reaction from His. Experiments confirmed that the adsorbed film can be removed and the electrode surface reactivated using brief polarization at +2.5 V. (C) 2007 Published by Elsevier Ltd.