A comprehensive experimental investigation on the effect of resonant length and the opening angle of harbour walls integrated with an Oscillating Water Column (OWC) under random sea state has been carried out. The random sea state is entitled to be the reference parameter for analysing the performance of the OWC under controlled conditions. The results on the variations of volume flux of water inside the OWC chamber, pneumatic pressure and relative capture width are depicted as a function of relative water depth for different configurations of the harbour walls in a dimensionless form. The presence of the harbour walls has enhanced the performance characteristics of the OWC. Further, the length and inclination of the harbour walls were varied to achieve a relative capture width, RCW (ratio of output power to the input power) of 75% more than that from the OWC without harbour walls. The details of the models, experimental set-up, testing procedure, results and discussion on the aforementioned study are presented.