The mesh-free code DualSPHysics is applied to simulate the interaction between sea waves and an Oscillating Water Column device (OWC). In this work, capabilities and limitations of DualSPHysics are shown in simulating OWCs. On the one hand, the new capabilities of DualSPHysics are shown by simulating the effect of mooring systems on a floating offshore OWC. On the other hand, simulations only consider a single-phase (water) so that the full OWC behaviour is partially reproduced, i.e. air pressure fluctuations are not modelled. The model was first validated with one laboratory test that consists of a fixed OWC with an open chamber. Next, water surface oscillations inside the chamber of a real OWC (located in Mutriku, Spain) have been predicted using the prevalent wave conditions observed in the area. Finally, the capabilities of DualSPHysics were demonstrated by simulating an offshore OWC moored to the seabed.