Because of their rapid construction and cost-effectiveness, mechanically stabilized earth (MSE) walls are one of the most preferred wall types in many civil engineering projects. As part of an attempt to reduce wall deformations, researchers have been studying the effect of properties of wall components, such as backfill soil stiffness and facing unit rigidity. The effect of concrete key size on wall deformations was investigated in this study using numerical analysis. Currently the concrete key is used for an alignment and leveling of the facing units. The effect of concrete key size for varying reinforcement lengths and foundation soil friction angles was studied. Numerical analyses were performed using Plaxis, commercially available finite element software. The results indicated that longer key lengths result in decreased wall deformations. The effect of the longer key lengths in reducing wall deformations was more significant for the walls with shorter reinforcement lengths and for the walls placed over weaker soils.