Ultra-High Molecular Weight Polyethylene (UHMWPE), classified as semi-crystalline thermoplastic, offers many outstanding material attributes such as high specific strength, high impact resistance and high resistance to corrosion; therefore, plates made of UHMWPE are widely used as load - carrying components in numerous application fields like automotive and military. In those applications, UHMWPE plates are generally subjected to dynamic loads; therefore, understanding their actual operating conditions under dynamic loads is crucial for robust design. To this end, very significant dynamic parameters, such as first three natural frequencies and corresponding mode shapes and damping ratios, that provide in-depth information regarding a dynamic material behavior were determined for UHMWPE rectangular plates with and without cut-out hole by conducting the modal analysis. While the dimensions of both rectangular plates are 150x100x4 mm, the diameter of the cut-out hole is 25 mm. Additionally, one side clamped boundary conditions were dictated to both plates during modal analysis. The first three natural frequencies and corresponding mode shapes wereextracted for both rectangular plates from Lancsoz eigensolver utilized in Abaqus software. Both experimental and numerical results revealed that the cut-out hole leads to a stiffness reduction in the UHMWPE rectangular plate which results in lower natural frequencies compared to the natural frequencies of UHMWPE rectangular plate without cut-out hole. Furthermore, as a result of the stiffness reduction caused by the cut-out hole, damping ratios calculated based on the half-power bandwidth were found to be less for the rectangular plate with cut-out hole. Nevertheless, it was also revealed that the pattern of structural deflections (mode shapes) is not influenced by the cut-out hole. The experimental results were favorably compared to the numerical predictions .