PURPOSES: The aim of this paper is developing user-oriented flexible Level Of Service (LOS) system for integrated asset management of various road facilities. It is essential to overcome limitations of general management systems which only focus on a type of assets (e.g. pavement, bridge etc.), and to serve a customizable LOS platform for smooth implementation and future improvement of the LOS considering various managerial environments of road agencies. METHODS: This study suggested a total framework of the LOS system as a process for self-development, operation and improvement of LOS system to conduct the PDCA (Plan-Do-Check-Act) in management process. In the process, we adopted user-customizable elements regarding asset definition, service index and evaluation method to match with the managerial environment of road agencies. In addition, we conducted an empirical study on the entire process of the suggested LOS system with a real road agency (Korea Express Highway) to prove applicability of the LOS system. RESULTS: From the empirical study, we confirmed that the suggested LOS system framework were suitable for development of customized LOS system. In addition, evaluation of asset conditions by LOS ratings, and quantification of vision achievement of the Korea Express Highway were successfully made. It would be the first trial in integrated management approach with LOS systems for numerous road facilities. CONCLUSIONS : It was recognized that easy application and sustainable improvement of the LOS was the most critical point in asset management. The suggested LOS system would be a powerful weapon as a managerial tool in preparing tight budget, aging infrastructures, and increased demands for more accountability both in Korea and internationally. Implementation of the LOS system needs to be expanded to the other infrastructure members to serve satisfactory level of service to taxpayers.