HfC whiskers are obtained on graphite substrates by a catalyst-assisted vacuum chemical vapor deposition process from the HfCl4-C3H6-H-2-Ar system in a reactive atmosphere containing a small amount oxygen impurity. The composition, crystallinity and morphology of the HfC whiskers are examined with energy-dispersive X-ray, X-ray diffraction, field-emission scanning electron microscopy. The influence of the element oxygen on the composition, crystallinity and morphology of the whiskers or deposits is analyzed. The results show that with the decrease of oxygen content during deposition, the quantity of HfO2 decreases and the crystallinity of HfC crystals improve, and the deposits change from the porous HfO2 coating covered by the HfO2 nano-rods into the HfC whiskers with rough side faces. Small HfO2 nano-particles grow on the surface of the HfC whiskers sporadically and dispersedly, and the sizes and quantities decrease as the O content reduces. Gibbs free energy of HfO2 generation is analyzed using HSC chemistry (R) 5.0. The results of the thermodynamic analysis confirm a small quantity of O can lead to HfO2 generation and HfO2 can stably exist under the reducing atmosphere with C3H6 and Hy at 1573 K. (C) 2013 Elsevier B.V. All rights reserved.