The effect of Cu content on hydrogen reduction behavior of ball-milled WO_3-CuO nanocomposite powders was investigated. Hydrogen reduction behavior and reduction percent(alpha) of nanopowders were characterized by thermogravimetry (TG) and hygrometry measurements. Activation energy for hydrogen reduction of WO_3 nanopowders with different Cu content was calculated at each heating rate and reduction percent(alpha). The activation energy for reduction of WO_3 obtained in this study existed in the ranging from 129 to 139 kJ/mol, which was in accordance with the activation energy for WO_3 powder reduction of conventional micron-sized.