In practice, in some cases, tandemly applied pile-mounted horizontal or inclined thin plates emerge as functional coastal structures in terms of diminishing wave height in front of Rubble Mound Breakwaters (RMBs) and consequently, reduce the required armor unit size and RMB's overall weight. In this study, the hydrodynamic performance of an Inclined Thin Plate (ITP) under regular waves is experimentally investigated. The objective of the laboratory experiments is the assessment of the ITP's efficiency in terms of wave attenuation. Various inclination angles in combination with different submergence degree of the structure under various wave conditions are examined. Regarding the examined ITP configurations, three different inclination angles are considered, i.e. 5, 10, and 15 deg as well as a horizontal plate on the free surface. For the inclined configurations, ITP was placed in a manner such that 2/3 and 3/4 of its length was submerged. The findings revealed that the transmission coefficients can be reduced down to 0.2-0.3. The findings revealed that a tandemly applied ITP has great functionality in diminishing the wave height at the seaward side of a RMB. In this way, the overall weight of the RMB and the weight of the armor units of the RMB are markedly reduced, which is highly necessary in cases where the foundation stability is poor.