Diamond particles 3–7 μm in size sustained in plasma in a high-dispersion state were coated with cobalt by magnetron sputtering. The relative concentration of cobalt in obtained powders was 2–3 mass. %. Sintering the diamond powders with the cobalt coating under the pressure of 8 GPa and the temperatures of 2000–2100 K resulted in the production of homogeneous specimens having the density of 3.6 ± 0.1 g cm − 3 . The produced diamond compacts demonstrated high values of the ultrasonic wave propagation velocity and elastic moduli.