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Recently, the importance of structural maintenance has been widely recognized. In order to establish a rational maintenance program, it is necessary to develop a cost-effective decision-support system for the maintenance of existing infrastructures. Life-Cycle Cost (LCC) is an useful concept in reducing the overall cost and achieving an appropriate allocation of resources.In general, Life-Cycle Cost optimization is to minimize the expected total cost which includes the initial cost involving design and construction, routine or preventive maintenance cost, inspection, repair and failure cost. Then, the optimal strategy obtained by LCC optimization can be different according to the prescribed safety level and required service life. In this paper, an attempt is made to discuss the relationships among the minimi~ation of LCC, the optimal extension of stuctural service life, and the target safety level by using the multi-objective Genetic Algorithm (GA). Namely, the following three objective functions are employed: 1) LCC is minimized. 2) Service life is maximized. 3) Target safety is maximized. By introducing the multi-objective GA, it is possible to obtain several available solutions that have different structural life spans, safety levels and LCC values.