At the point, which it becomes more expensive to extend the service life of vehicle than owning and operating a new one, it becomes economic to replace it by a new one, present less operating costs, less out of working periods and more income. However the procedure of replacement vehicles, after determining the optimal economic lifetime, are very useful, where decision makers are facing with complex tradeoffs involving economic, environmental, or policy impacts of fleet management decisions or regulations. This paper reports a scientific concept, for replacing or choosing vehicles. Several widely microbus vehicles run in ministry of health, ambulance sector, Egypt, are used in this study. The results indicated that each vehicle has its own history, so the best time to get rid of one vehicle is not necessarily the best time to get rid of other vehicles of the same age and type. In addition, the decision of replacement is part of a wider problem involving many factors other than depreciation and maintenance costs.