The present study has been performed to evaluate the heat transfer performance of a rim seal which is used to prevent the hot gas ingestion into the gas turbine disks. The fluid flow and heat transfer characteristics in the rim seal have been analyzed using three-dimensional Reynolds averaged Navier-Stokes equations. The Reynolds number based on the axial chord at the mainstream outlet was fixed at 500,000. The one-equation Spalart-Allmaras turbulence model was used as the turbulence closure model through the turbulence model test. Computational results for the sealing effectiveness on a specific control plane have been validated compared to the experimental data under the same condition. The sealing effectiveness enhances as the leakage fraction and the rim seal inlet velocity increase. To examine the effect of the rim seal configurations on the sealing effectiveness, different types of rim seal have been tested in this study. The newly designed rim seal shows remarkably improved sealing effectiveness compared to the reference design.