MnOx was synthesized through the oxidation of MnCO3 and its catalytic activity in the complete oxidation of ethanol was determined. Analyses of the catalyst through in situ X-Ray Diffraction and in sine DRIFTS spectroscopy showed the presence of Mn2O3 (bixbyite) and gammaMnO(2). The catalytic activity of MnOx depends on the mixtures of oxides and the treatment before reaction.