The Mononobe-Okabe (M-O) method based on limit equilibrium principle is widely used in the design of retaining structures against earthquake loads. However, this method does not consider the soil-structure interaction and wave propagation effects. On the other hand, it is known that the interactions of retaining structures with backfill and foundation soils transform the seismic behavior of these structures to a rather complex problem. The main purpose of this study is to evaluate the soil-structure interaction and wall flexibility effects on the seismic behavior of backfill- cantilever retaining wall-foundation/soil systems. In line with this target, three dimensional finite element models were utilized for analyzing the aforementioned systems. Seismic analyses were carried out in the time domain by considering five different foundation soil conditions and two different wall thicknesses. The results were comparatively interpreted in terms of lateral wall displacements and the stresses occurring at critical sections of the wall. It was observed that these responses may vary significantly due to soil-structure interaction and wall flexibility effects.