Arsenic element refines W powders significantly during the hydrogen reduction process of tungsten oxide in our previous studies. In this paper, the nanocrystalline WC-As composite powders were prepared by carbonization of nano W-As composite powders and the effects of arsenic on the growth of WC powder were discussed in detail. The prepared samples were characterized by X-ray diffraction, differential scanning calorimetric analysis, scanning electron microscope, transmission electron microscope, X-ray photoelectron spectroscopy and Inductively Coupled Plasma. The results showed that arsenic appropriately raised the initial temperature of carbonization, significantly accelerated carbonization reaction process and shorten the reaction time. Moreover, WC-As composite powders merged and grew up directly without particle expansion and cracking. And the nano WAs2 particles attached to WC grain boundaries and hindered the growth of WC grain through grain boundary migration. The above two effects resulted in the WC-As composite powders prepared at 1300 degrees C for 2 h with the average size of about 121 nm in diameter. (C) 2018 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.