A multi-user relational data base management has been developed in KAIST and this system consists of three level interfaces which are User interface, High-level interface, and Low-level interface. In this thesis, only the User interface and High-level interface are studied, primarily. The User interface aims at a management of users, a system protection, and a SQL language translation. And, the High-level interface is mainly concerned with an authorization mechanism, a language process mechanism, and a query optimizer. This system was implemented in PL/I high level language on VAX/VMS which is the operating system of the VAX-11/780 supermini computer.