Electrochemical killing of Escherichia coli cells was carried out using oxidized form of ferrocenemonocarboxylic acid (FCA) dissolved in 0.1 M phosphate buffer (pH 7.0). Cyclic voltammetry of 0.25 mM FCA was performed with the addition of coenzyme A (CoA), that is considered to be the main contributor of the anodic peak current appeared at around 0.7 V vs saturated calomel electrode in cyclic voltammogram of microorganisms. Electrocatalytic oxidation of CoA was observed at around 0.3 V. Also, the electrocatalytic oxidation wave was confirmed when cyclic voltammetry was performed in 0.25 mM FCA containing 1.7 x 10(11) E. coli cells/ml. Electrochemical killing of E. coli was examined by applying constant potentials-in 0.5 mM FCA. The survival ratio decreased to below 5% at low potential of 0.4 V in 0.5 mM FCA compared to 0.7 V in the buffer. The decrease in survival ratio was also observed with the gram-positive bacterium, Bacillus subtilis and an eucaryote cell, Saccharomyces cerevisiae. When E. coli cell suspension was added to 0.5 mM FCA, oxidized by applying 1.0 V for 60 min, the decrease in survival ratio was observed. In contrast,decrease in survival ratio was not observed when cell suspension was added in FCA without electrolysis. E. coli cells were shown to be killed by the contact with oxidized form of FCA.