The cross-sections of Reinforced Concrete (RC) members are assumed in the preliminary design. With optimization, optimum dimensions of cross-sections providing required security measures can be obtained. Although, the area of the reinforcement bars is a computable value according to the cross-section, the amount and size of bars are also design variables in order to ensure the placement of bars providing adherence and other physical conditions. In this paper, the optimum design of RC continuous beams is presented by considering design constraints given in ACI-318 (Building Code Requirements for Structural Concrete). The most critical stress resultants of continuous beams are computed for all live load distribution patterns using three moment equations and were used in the analysis of continuous beam. A Random Search Technique (RST) is developed in order to minimize the material cost of the continuous beam. The RST is employed in different stages of optimization process such as cross-section and reinforcement bar optimization. The approach is effective to find the detailed optimum design of RC continuous beams with minimum cost.