This paper presents a synchronous generator out-of-step detection using a Fuzzy Logic (F.L) based approach. After obtaining the convenient state variables (generator prefault loading , difference in acceleration and the average acceleration), three different OS schemes can be designed using the proposed F.L technique. These three schemes correspond to the possible alternatives of selecting two features out of three primary variables. The proposed technique is applied for two different study systems. It is found that once F.L based classifier is applied, accurate and fast decision about the case of the synchronous generator after certain system disturbance is obtained. The developed approach is implemented on Matlab-Simulink for case studies to emulate the real time implementation of the technique.