Abstract: The design of retaining structures often relies on the lateral earth pressure coefficient, and this method is widely used in practical engineering problems. The traditional approaches for calculating the lateral earth pressure coefficient are performed under plane-strain condition by ignoring the end effects posed by three-dimensional (3D) characteristics. Based on a 3D slope stability analysis, the variational limit equilibrium analysis is used to obtain the minimum factor of safety and its corresponding critical 3D failure mechanism. The object of this study is to propose a procedure for calculating the lateral earth pressure in block-faced soil slopes considering 3D effects and to investigate the 3D effects on the lateral earth pressure. The soil-facing interface friction and horizontal seismic forces are also considered. The results are presented in the form of charts that give the lateral earth pressure coefficients from an extensive parametric study in which various ratios of length to height are used. An optimization procedure is employed. It is found that the impact of seismicity is significant, especially for the vertical retaining structures. An example is also given to demonstrate the difference in the lateral earth pressures obtained from the classic earth pressure equation and 3D analyses, showing the importance of 3D effects on lateral earth pressure coefficient in retaining structures.