Despite the high electrocatalytic activity of Pt, pure Pt electrocatalysts always suffer from high cost and poor poison resistance. In this work, a cubic PtPdCu nanocage (NC) trimetallic electrocatalyst was synthesized using cuprous oxide as a sacrificial template. Being employed as a H₂O₂ detection electrode, PtPdCu NCs exhibit higher sensitivity (562.83 μA mM⁻¹ cm⁻²) than that of PdCu NCs (210.19 μA mM⁻¹ cm⁻²), PtCu NCs (411.34 μA mM⁻¹ cm⁻²) and commercial Pt black (16.94 μA mM⁻¹ cm⁻²). Furthermore, a PtPdCu NCs electrode presents a working potential as low as 0.05 V. The excellent electrocatalytic activity can be attributed to the suitable hollow porous structure and synergistic electrocatalysis effect between Pt, Pd and Cu. It is believed that the trimetallic PtPdCu NCs electrocatalyst has potential applications in the design of H₂O₂ detection electrodes.