Abstract A performance of an energy-efficient reverse osmosis (RO) system for seawater desalination was evaluated. The evaluation focused on energy saving performance of the RO system. The strategy adopted was to induce high recovery (50%) through the pressure increase. For this purpose, a pilot-scale RO plant (5 m 3 /h) was built and installed in a southern port of Korea. The study showed that energy saving was possible by application of high pressure. The 50% recovery was achieved at 8.3 MPa, but the operation led to water quality degradation. The water quality problem was solved by the operation of two-stage mode. Under this condition, the target recovery was achieved at lower pressure (6.6∼7.5 MPa), which resulted in the saving of power consumption. No water quality degradation was observed. Further saving was possible by adding energy recovery turbine (ERT) and inverter system. When the RO system was operated for 50% recovery at two-stage mode while equipped with energy saving devices of ERT and inverter system, 44% of saving in power consumption was possible.