Using OBS (Off-center Bracing System) is one of the methods to make buildings resistant to the lateral Loads. This kind of brace has a great tendency to out of plane buckling. So, due to the lack of formal regulations, analyzing out of plane effective length of its members is important. In this paper, buckling load of 15 one-story frames is obtained and then out of plane effective length factor of the longer member is calculated. Finally, as buckling of one of the members causes the system to lose its stability, the mentioned effective length factor is introduced as out of plane effective length factor for all OBS members.