Recently, lack of nurses and care nurses is a serious problem because of the increasing demands of nursing care for age people. So, indoor robot navigation system is important as one of the possible robot technologies to compensate for the lack of nurses. In particular, an indoor robot navigation system using the RFID system which is easy configuration and cheap relatively is studied all over the world. But these studies have assumed an ideal environment. For example, there are not any obstacles. To avoid obstacles, location estimation method and the moving control method that considered the surrounding environment are desired. In this paper, we propose a new indoor robot navigation system that is composed of passive RFID system to avoid obstacles. In this system, we install a passive RFID tag with an obstacle and store the information of the obstacles in the tag. A mobile robot avoids the obstacle by using the information. We performed experiments of a mobile robot to show the effectiveness of the proposed system. As a result, it is shown that it is possible to avoid the obstacle by the proposed system.