An integrated breakwater-WEC system, which comprises of an array of heaving Oscillating Buoy Wave Energy Converters (OB-WECs) attached at the weather side of a fixed breakwater, is proposed in this study. Detailed experiments have been undertaken to investigate the heave-response-amplitude operator (HRAO), the wave force on the WEC devices and the transmission coefficient of the breakwater-WEC system. The design of the experiment is validated by comparing the HRAO of the devices with the corresponding numerical results. The hydrodynamic performance of the breakwater-WEC system is compared with that of its isolated counterparts, i.e., the isolated WEC array and the isolated breakwater. Parametric studies are conducted to optimise the draft of the WEC devices and the breakwater-WEC spacing, i.e. the gap between the WEC devices and the breakwater. Results show that, compared with the case of isolated WEC devices, the wave force and HRAO of the WEC devices are amplified for a properly designed breakwater-WEC system. Even though the external damping (caused by viscous damping and the friction loss) plays an important role while evaluating the efficiency of the WECs, the existence of the breakwater significantly improves the performance of the WEC array. The HRAO is sensitive to the draft of the devices and breakwater-WEC spacing.