Oscillating water column (OWC) wave energy converters (WECs) have two energy conversion stages. In this study, an axial-flow impulse turbine was installed on an OWC model to replace the traditional substitute, such as the orifice plate. The OWC model was placed in a wave flume for the experimental tests under regular wave conditions. This experimental setup was expected to reflect more actual interactions between two stages at the model-scale level. During the tests, various constant rotation-speeds of the impulse turbine were controlled by a servo motor. The free water-surface elevations at different positions in the OWC model, the air-pressure variations in the chamber, and the torque output of the turbine were recorded. The time histories and phase relationship of typical measured data were analyzed. The primary-stage and secondary-stage efficiencies were calculated under various wave conditions. The overall efficiency of the model peaked at the resonant length ratio of 7.1. All the experimental results can be employed as typical benchmarks for an accurate validation of numerical models.