Exploring effective electrocatalysts is in urgent demand to boost their large-scale applications for direct ethanol fuel cells. Herein, for the first time, we report nanoparticle-assembled Pd nanocages with efficient catalytic activity towards ethanol electrochemical oxidation. The catalysts are prepared from the second template of a nanosheet surface of amorphous Co(OH)₂ octahedral nanocages, which are prepared from the original template of octahedral Cu₂O. These Pd octahedral nanocages exhibit a porous rough surface, which consists of smaller Pd nanoparticles, endowing them with highly active surface area and many active sites. For the electrochemical oxidation of ethanol, the Pd nanocages demonstrate superior activity (3765 mA mg_Pd⁻¹), 4.8 times and 5.9 times those of commercial Pd/C and Pd nanocatalysts, respectively, prepared directly from an octahedral Cu₂O original template. Furthermore, the Pd nanocages demonstrate excellent long-term durability.