A photoanode exhibiting high water-splitting efficiency at low bias potential is essential for stand-alone water-splitting devices through a tandem system combined with a photovoltaic device. However, many previous studies employing a typical BiVO4/WO3 heterojunctions focused on water oxidation at the maximum thermodynamic water splitting potential, 1.23 V vs. the reversible hydrogen electrode (VRHE). Here, we suggest a strategy for high water oxidation efficiency at low potential using 3D BiVO4/ZnO heterojunction photoanodes. The BiVO4/ZnO heterojunction exhibits a lower onset potential compared to the commonly used WO3 heterojunction. Due to the 3D ordered structure, the BiVO4/ZnO achieves enhanced light harvesting efficiency and improve charge separation efficiency at low bias potential by ZnO heterojunction. As a result, the BiVO4/ZnO photoanode exhibits a water-splitting photocurrent density of 3.3 ± 0.2 mA /cm2 is obtained at 0.6 VRHE under 1 sun illumination.