Site-selective deposition of dual cocatalysts for H2 and O2 evolution reactions on polymeric carbon nitride (PCN) nanosheets still remains a great challenge due to the difficulty in controlling the nucleation location and growth dynamics. Herein, we report an one-step and efficient photodeposition strategy to simultaneously load Rh and RhOx nanoparticles on PCN nanosheets with desired spatial isolation. The dual cocatalysts modification can effectively accelerate the reaction kinetics and boost the separation of photoinduced charge carriers, greatly enhancing overall water photosplitting efficiency. As a result, the overall water photosplitting activity of Rh-RhOx/PCN is obviously higher than those of RhOx/PCN and Rh/PCN. This work provides a new method for loading dual cocatalysts on the PCN nanosheets with spatial isolation to achieve pure water splitting under visible light and offers promise for a wealth of innovative applications in energy conversion, catalysis and environmental protection.