Abstarct: Eccentrically braced frxames (EBF) provide resistance loading system which has both the advantages of Moment Resistant frxames (MRF) and cocentrically braced frxames (CBF) simultaneously. In this research, the role EBF bracing in moment frxames is investigated. In other words, the effect of EBF in controlling the deformation and failure mechanism of moment frxames is compared with the moment frxame alone. The structural models used this research are two dimentional moment frxames with eccentrically braces. The models are 5, 10 and 15 storeis frxames with 4 spans and the different ratios of lixnk length to span length equals 0.15 , 0.2 and 0.25. lixnk beams in the frxames are short hence the shear behavior can be expected. A total of different configurations (models) are investigated. The nonlinear behavior of the models is studied through plastic joint formation and the effect of EBF on reducing deformation and drift is studied. The frxames first were analysed and designed by Etabs software then the nonlinear analysis of the frxames were attained by using Sap2000 software which has high capability in nonlinear analysis. The ATC40 and FEMA273 conditions have been included.