Problem statement: Moment Resisting Frame (MRF) is widely used as lateral resisting systems when sufficient ductility and deformability are to be met. Response of these structures is strictly dependent upon behavior of their joints, whereas the analysis of steel moment resisting frames generally has been performed without considering the accurate connection behavior. Approach: In this study Finite Element (FE) models had been developed to obtain the moment-rotation relations of theoretically fixed connection types which were widely utilized in Iran. Using moment-rotation relation obtained from FE analysis, 2D global structural model of MR buildings were developed afterwards to evaluate the behavior of the structures globally. Nonlinear static and dynamic analyses were carried out subsequently to investigate the structural behavior of MRFs having built-up column sections. Results: The results proved considerable effects of beam column connection behavior on nonlinear response of structures. Conclusion/Recommendations: It was recommended to consider the effects of connection properties in analysis and design of the MRF.