A two-dimensional finite-element analysis based on PLAXIS 2D was used to study the behavior of connected and unconnected back-to-back mechanically stabilized earth walls under earthquake loading. The numerical model was first validated with the results from the full-scale dynamic centrifuge tests on reinforced soil-retaining walls. The behavior of connected and closely spaced unconnected back-to-back mechanically stabilized earth walls (BBMSE) was compared in terms of tensile forces mobilized in geogrids, and the lateral earth pressures and maximum displacements of the wall. The total seismic earth thrusts at the end of the reinforced zone and at the facing of BBMSE walls and their points of application were presented. These results were compared with the widely used Mononobe-Okabe method. The connected walls were found to significantly reduce the dynamic loads on the walls compared with those on unconnected walls. © 2021 American Society of Civil Engineers.