The electrochemical hydrating/dehydrating behavior of MmNi(5)-type alloy electrodes in an alkaline solution was investigated with cyclic voltammetry, scanning electron microscopy and X-ray photoelectron spectroscopy analysis. At an Mm(Ni3.8Co0.5Al0.4Mn0.3)(5) powder microelectrode, a hydrogen absorption peak was observed at more negative potential than that of the water electroreduction and hydrogen adsorption peak in its cyclic voltammograms. In addition, the electrochemical mechanism of the hydrogen absorption and desorption at the hydride electrodes in the alkaline solution is discussed.