In this paper a Fuzzy Discrete Event Systems (FDES) based approach is proposed to behavior coordination of a mobile robot moving in unknown environments. Fuzzy controllable and uncontrollable events are newly defined to activate deliberative and reactive behaviors of the robot respectively. A fuzzy supervisor is defined to control the FDES by partially activating fuzzy controllable events with fuzzy uncontrollable events simultaneously, to achieve the planned objectives. In order to incorporate uncertainties of the associated sensory system, fuzzy observability is introduced into each fuzzy event, and the existence of a fuzzy partially observation supervisor is discussed. The control theoretic properties of the system such as fuzzy state based controllability and observability measures are also introduced. The effectiveness and efficiency of the proposed method are demonstrated with both simulation and real time implementation.