Despite the fact that the monodisperse cobalt boride particles prepared in CTAB / 1-hexanol / water reversed micellar systems are the quite small particles with a narrow size distribution, they exhibited little hydrogenation activity in reversed micellar solution. The chief cause are due to combined effect of both adsorption of the CTAB molecules on the catalyst and the slow transport process of hydrogen from the organic phase of the reversed micellar solution to the surface of catalyst. The experiments have revealed an interesting fact that addition of ethanol to the reversed micellar solutions simultaneously lead to the increase in catalytic activity and coagulation of catalyst particles.