The growth of oxidized Mg layers on Co(0001) single crystal was studied using X-ray photoelectron spectroscopy (XPS), thermal desorption spectroscopy (TDS) and low energy electron diffraction (LEED). Magnesium was evaporated in metallic form and oxidized by preabsorbed oxygen diffusing to the surface from the subsurface region of the Co crystal. The simultaneous multilayers mechanism of the film growth was observed by the comparison of XPS and TDS data. No LEED pattern was observed from the overlayer. The first layer grew as MgO and the next layers as MgOx (x≈ 0.5). Partially oxidized MgOx on Co(0001) dissociated CO resulting in fully oxidized MgO. The TDS results showed blocking of adsorption sites by MgO.