As global awareness of environmental concerns associated with automobiles has grown significantly, Life Cycle Assessment (LCA) has emerged as one of the analytical tools to provide environmental information on automobiles throughout their life cycles. In order to be most efficient in terms of both environmental performance and cost saving, it is necessary to perform LCA studies within a short period of time in the automobile design stage. However, since an automobile consists of a great number of components, a full LCA of an automobile takes too much time and expense.The purpose of this paper is to introduce a practical, systematic LCA methodology for a whole automobile, with which a time and cost effective calculation can be ensured for a highly complex system. First of all, the entire automobile is divided into several modules, each of which is composed of 10-20 submodules. In this process, the concepts of part modularization and platform commonization are incorporated. The life cycle inventory for a whole automobile is obtained based on the ecological data of modules and submodules by using a combination of top-down and bottom-up approaches.