The electrochemical formation of spinel-type cobalt oxide has been presented in which the potentiostatic or potentiodynamic oxidation is performed with a Au or Pt electrode in a solution of high pH containing CoSO4 and glycine. The electrochemical quartz crystal microbalance studies indicate that the electrodeposition of cobalt oxide proceeds through the electrochemical oxidation of a cobalt-glycine complex at high pH. The scanning electron microscopy morphology of the deposited film is very compact and quite similar to that of the cobalt oxide prepared by the sol-gel route, followed by the heat-treatment around 300degreesC. The constituent of the film is determined to be Co3O4 from the electron probe microanalysis and X-ray diffraction measurement. The electric charge of 350 mC cm(-2) passed at 1.0 V vs. Ag/AgCl in a solution of pH 10.5 containing 2 mM CoSO4 + 20 mM glycine corresponded to the film thickness of 10 nm. The Co3O4 -deposited Au electrode exhibits two reversible couples in an alkaline solution. The first observed at 0.120 V is attributed to the redox of CoOOH/Co3O4, and the second appearing at 0.476 V is equivalent to the CoO2/CoOOH couple.