In this study, optimum design of cantilever reinforced concrete cantilever retaining walls is investigated under static load conditions. A methodology based on a recently developed metaheuristic algorithm called grey wolf optimizer was proposed. As the objective function, the total cost of the retaining wall including concrete, steel, labor, transportation etc. is considered. The eleven design variables such as heel and toe projections, stem thickness at the top and bottom of the wall, slab thickness, diameters and spacing of reinforced bars in critical sections are considered in the optimization process. During the optimization, totally twenty-nine design constraints including overturning stability, sliding stability, bearing capacity (maximum and minimum soil stresses), flexural moment and shear capacities of the section, minimum and maximum reinforcement ratio, development length of the bars, spacing limits of the bars (maximum and minimum spacing) are checked for the security of the wall. The requirements of the American Concrete Institute (ACI 318 14: Building code requirements for structural concrete) are considered in the reinforced concrete design.