The objective of this study is to develop a design decision support tool that incorporates life cycle costing including the environmental effects of a system. A life cycle costing that incorporates the effects of the environment is essential to support the design decisions required during today''s product or system developments. Since the international environmental standards (ISO 14000 Series) were issued in the early 1990s, the leading companies in the automotive industry have been developing integrated assessment methodologies. These methodologies attempt to integrate cost, quality, environment and other related areas into the total life cycle assessment of a system. Therefore, it is important to develop a tool that integrates all information concerning the product in the early stages of development. It is also appropriate to support the decision-making in selecting the best design alternatives. The tool can minimize the trade-off between technical performance and cost parameters using an integrated database that includes all relevant information. The development approach is based on the Activity Based Costing (ABC) that is essential for new management culture of modern enterprises. The tool adopts the object-oriented software structure and utilizes the Unified Modeling Language (UML) to model the architecture. From a technical point of view, the tool can be utilized at early stages of development in order to assess the life cycle cost to get a higher level of productivity. A door trim example of LCA and the environment costing results was demonstrated to present the concept.