Diamond was deposited on an Mo substrate placed in CO2-CH4-Ar and CO2-CH4 microwave plasmas. In these plasmas, larger amounts of CO and OH radicals were identified than those of CH and C-2 radicals by OES. Strong peaks due to CO and H-2 were identified by means of QMA. The surface temperature of the substrate was about 1150 +/- 20 K. Particles exhibiting cube-octahedral habit planes were observed in SEM images. The sharp lines due to diamond were identified in X-ray diffraction patterns and Raman spectra. The adsorption of CO on the surface of the deposit from the CO2-CH4 microwave plasma was identified by XPS at the beginning of the deposition. Diamond could be deposited from the CO2-CH4 microwave plasma through the adsorption of CO molecule as precursors.