The synthesis of W-l5wt%Cu nanocomposite powder by hydrogen reduction of ball milled W-Cu oxide mixture was investigated in terms of powder characteristics such as particle size, mixing homogeneity and micropore structure. It is found that the micropores in the ball milled oxide (2-50 nm in size) act as an effective removal path of water vapor, followed by the formation of dry atmosphere at reaction zone. Such thermodynamic condition enhances the nucleation of W phase but suppresses the growth process, being in favor of the formation of W nanoparticles (about 21 nm in size). In addition, the superior mixing homogeneity of starting oxide mixture turned out to Play a significant role for forming extraordinary chemical homogeneity of W-l5wt%Cu nanocomposite powder.