Our group has developed diamond film synthesis in vapor phase by the so-called magneto-active microwave plasma chemical vapor deposition. The goal of the diamond film growth over large area at belwo $200^{circ}C$ with high quality has been tried rather successfully. The growth rate can be enhanced by pulse modulated discrage which enables us to control radical densities in the plasma. Thermal flux to the substrate from the palsma can be reduced with decreaing the duty ratio of the discharger resulting in cooling down the substrated for the low temperature deposition. Nanocrystal seeding is Essentially and unique pretreatment for diamond nuclei to improve the film quality. Such high-density and high-quality nuclei due to the seeding with purified nanocrystalline diamond paricles can be realized netither through scratcihing norbiasing at low temperature, e.g., below $200^{circ}C$ .