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Abstract: In this paper, we report the effect of gaseous carbon dioxide (CO2) introduced in the typical reaction atmosphere of CH4/H2/N2 (60/500/1.8 in sccm) on the growth rate, morphology and optical properties of homoepitaxy single crystal diamonds (SCDs) by microwave plasma chemical vapor deposition. The additional carbonaceous sources supplied by CO2 are favorable to increase the growth rate, and meanwhile, the oxygen related species generated would enhance the etching effect not only to eliminate the non-diamond phase of SCD but also to decrease the growth rate. The appropriate addition of CO2 can increase the high growth rate, decrease the surface roughness, and reduce the concentration of N-incorporation. It is demonstrated that adding CO2 strongly affects the contents of various reaction species in plasma, which would determine the growth features of CVD SCDs. [Copyright &y& Elsevier]