The Manufacturing System Design requires a clear knowledge of the system and the lnformation System support (qualitative and quantitative) necessary for evaluating and deciding among different design alternatives. A fundamental aspect during the design process is to develop a model which describes the system, with the required detail level, and in a formal, concise and suitable way, in order to study the impact of the decisions on the system performance, before its construction. Among different modeling methodologies applicable to Manufacturing Systems, Object-Oriented Methodology stands out for its capability of representing at once organizational, technological and human aspects involved in a complex production system, and of modeling its dynamic dependencies as well. This paper shows a new way to develop a model using an Object-Oriented Methodology, called RCOO, developed by the IRIS Group of the Universidad Jaume I and the GIP Group of the Universidad Politecnica de Valencia, and apply it to develop a Reference Model of a Manufacturing System, that can be used to simulate different alternatives of a particular Manufacturing System. This research work has been sponsored by the CICYT (Comision Interministerial de Ciencia y Tecnologia), inside the TAP Project Number 0880.