Abstarct: The feasibility of weigh optimization of multi-span non-prismatic girder plates under various static loadings with genetic algorithm (GA) was studied. A computer code baxsed on matrix structural analysis techniques has been developed to find the internal forces due to the specific loading, cross sections, and number of spans. The genetic algorithm was employed to find the beam span, wall thickness, width and thickness of flanges in selected positions. In this thesis after reviewing the literature, the fundamentals of GA were presented. The design criteria and the method to find the optimized section baxsed on GA were described. To illustrate the method, several examples were given and the results were compared with available cases in the references to evaluate the method.