Ultra-high temperature ceramic zirconium carbide (ZrC) nanopowders were synthesized for the first time via a microwave-assisted carbothermal reduction reaction using zirconia (ZrO2) and carbon black (C) as the starting materials. The effect of the reaction time on the formation of ZrC nanoparticles was examined. The as-synthesized samples were characterized using X-ray diffraction (XRD), helium pycnometry, Brunauer-Emmett-Teller (BET) N-2 adsorption, scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). The lattice constant and interplanar distance (d(111)) were calculated, and the crystallite size was obtained using the Scherrer formula. Results from the experiment show highly crystalline ZrC, with crystallites less than 50 nm and nearly-spherical morphology, using 3 kW of power and only 50 min of reaction time, with a maximum reaction temperature of 1400 degrees C, lower than those involved using the conventional heating carbothermal reduction. The reaction time was similar to 2 h shorter than that required by using a combined sol-gel and microwave-assisted carbothermal reduction method, used to prepare submicron ZrC powders (200-300 nm). The high heating rate achieved on the synthesis was favored by the excellent microwave absorption of carbon black, and the uniform heating at molecular level induced by the microwaves on the samples. (C) 2019 Published by Elsevier B.V. on behalf of The Society of Powder Technology Japan. All rights reserved.