A radio-frequency atmospheric-pressure plasma process has been applied to the synthesis of ultrafine ZrC powders using ZrCl4 and CH4 as precursors. Both thermodynamic analysis and experiments were conducted and the as-prepared samples were characterized by X-ray diffraction, electron microscopy, and laser scattering. Results showed that ZrC powders with particle size <100 nm and surface area of 36.56 M2/g could be obtained. The addition of excess H2 contributed to the increase in conversion rate. The conversion rate was about 65% when the carrier gas ratio (H2/CH4) was set at 4.0 and added axially through the injection probe.