As one of the most abundant renewable biomass resources, wood can be used as templates for synthesizing functional nanoparticles with controlled shapes and sizes. In this study, copper nanoparticles were synthesized with controlled shapes and sizes using poplar wood as the natural inexpensive and renewable templates. The crystal structure and morphologies of the copper nanoparticles were characterized by the X-ray diffraction and field emission scanning electron microscopy. Due to the hierarchical and anisotropic structure and electron-rich components of wood, pure copper nanoparticles were synthesized with fcc structure and uniform sizes, and then assembled corncob-like copper deposits along the wood cell lumens. The concentration of OH-1 had a larger effect on the products of nanoparticles. With the increase in OH-1 concentration, Cu2O gradually decreased and Cu remained. Due to the restriction of wood structure, the derived Cu nanoparticles showed the similar grain size in spite of the increased concentration of Cu2+. This combination of Cu nanoparticles and wood matrix could fabricate a wood-inorganic composite that exhibits unique characteristics.