Recently, the shipbuilding industry in the world market has become extremely the competitive. To compete in the global market, shipbuilders need to produce ships more efficiently. Therefore, the development of new methods like building series ships, design optimization, and modularization concepts is necessary. This paper presents a new approach for engine room design based on the modularization concept. The characteristics of the proposed method are as follows: Attention was paid to piping systems of multiple bulk carrier series of different sizes. The cost and weight of the piping system as well as the similarity and the commonness of the modules and arrangements were considered. The piping system design process was divided into two stages: module definition and arrangement design. To define an effective module that could be commonly used in different ships, a design structure matrix was adopted. In the arrangement design, an optimization system was developed using a genetic algorithm to obtain a similar pattern for module arrangement in multiple series ships with specific consideration toward the cost and similarity. This study discusses the details of the above mentioned methods. In addition, the piping system of an actual ship was designed using the proposed method and its effectiveness was evaluated.