Concrete-faced rockfill (CFR) dams are known as least-cost alternative of clayey core rockfill (CCR) dams. Although clayey core material is a natural choice, it can not be obtained from the environment of the project area continually. CFR dams have increasingly been constructed in many parts of the world because of high resistance to ground motions. As the new experiences regarding these dams have been acquired, design properties of concrete slabs are altered in the course of time. One of the main concerns of CFR dams is the seismic performance of concrete slab during an earthquake. Therefore, the effect of face slab thickness on seismic performance of concrete slab on a CFR dam is investigated in this study. Torul CFR dam is chosen for numerical applications. Five different slab thicknesses derived from the formulations preferred in the literature are taken into consideration. Dam-reservoir-foundation interaction system is modeled by the finite element method. Contact analysis is also integrated in finite element analyses using interface element in concrete slab-rockfill interface. Hydrodynamic effects of the reservoir water are considered by the Lagrangian approach. In the nonlinear time-history analyses, Drucker-Prager model is used for concrete slab and multi-linear kinematic hardening model is utilized for rockfill zones and foundation soil. 1992 Erzincan earthquake with peak ground acceleration of 0.515g recorded near the dam site is used in numerical analyses. Linear and nonlinear analyses are carried out for different face slab thicknesses. According to this study, the increase in face slab thickness clearly improves the seismic performance of the concrete slab on CFR dam.