We have investigated homoepitaxial diamond growth by high-power microwave-plasma chemical-vapor-deposition (MPCVD) method. The diamond growth rate R-g increased linearly with increase in the methane flow-rate ratio in the total source gas flow, C-me, only for C-me >4% while increasing non-linearly with the C-me for C-me <4.0% under the high microwave power condition of 3.8 kW. In the case of the present high-power MPCVD, saturation of R-g, that often occurred at C-me approximate to 1.0% in conventional MPCVD cases, was not observed in the whole C-mc range examined (less than or equal to32%). The crystalline quality of diamond films became relatively better and the surface morphology became smooth without non-epitaxial crystallites in the C-me range from 4.0 to 8.0% under the growth conditions. For R-g > 10 mum/h, however, formation of round-shape hillocks, various defects and vacancies including nitrogen-related CL centers occurred in some cases. It is found that these degradations, which occurred for C-me > 10.0% in the present MPCVD case, can be suppressed by increasing plasma density using higher microwave power of 4.7 kW and higher total gas pressure of 160Torr. Possible reasons for the observed advantages in the present high-power MPCVD method are discussed. (C) 2004 Elsevier B.V. All rights reserved.