Generally, in practice, effect of infill walls is not taken into account in the design or seismic performance assessment of RC buildings. In order to consider this effect, certain calculations and assumptions should be made. In this study, a simplified method, which considers this effect by employing a coefficient, is investigated and the criteria defined to employ this method is examined. A similar recommendation is investigated in detail given in the recent code namely "Determination of Seismically Vulnerable Buildings" in the context of "Urban Transformation Law", where a single coefficient was defined to consider the effect of masonry infill walls. Column shear forces, inter-story drift ratio, mode shapes and the corresponding periods are the engineering demand parameters used in the assessments. Analytical model of a four-story RC building is generated and the effect of infill walls on its seismic response is investigated. It was found out that the coefficient proposed by the code "Determination of Seismically Vulnerable Buildings" to consider the effect of infill wall leads to column shear demands that are on the safe side in most of the cases. On the other hand, unsymmetrical arrangement of infill walls can cause torsion in the structure, which increases the shear demands in certain columns. Accordingly, it is suggested to add a further limitation in the application of the simplified method in the relevant item of the code "Determination of Seismically Vulnerable Buildings" when the infill walls cause torsion in the structural system.